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Wind M, Bjelland M, Pérez-Rodrigo C, et al. Appreciation and implementation of a school-based intervention are associated with changes in fruit and vegetable intake in 10- to 13-year-old schoolchildren: The Pro Children study. Health Educ Res. 2008; 23(6): 997-1,007. 

PubMed ID: 18156147
Study Design:
Cluster Randomized Trial
A - Click here for explanation of classification scheme.
POSITIVE: See Research Design and Implementation Criteria Checklist below.
Research Purpose:
  • The first aim of this study was to investigate:
    • The quantity and quality of Pro Children activities that were implemented at school
    • The degree of parental involvement as indicated by the number of activities that were carried out with the parents
    • Exposure to fruit and vegetables as indicated by changes in weekly frequency of direct intervention-related distribution of fruit and vegetables in school
    • Appreciation of the project by the child
  • The second aim of the study was to assess whether the above four process measures were associated with the short-term effects of the intervention on children's frequency of fruit and vegetable intake.
Inclusion Criteria:

None specified, but the study included school children in 117 classes in 62 schools within three European countries.

Exclusion Criteria:
  • Children and parents who did not complete the surveys due to:
    • Lack of consent
    • Absence
    • Illness
  • Children who dropped out of the study
  • Children who over-reported fruit or vegetable intake (reported consuming more than 1,000g of fruit or vegetables in the previous day). 
Description of Study Protocol:


  • Surveys among children and parents were conducted prior to the intervention (September 2003), immediately after the intervention (May 2004) and at the end of the following school year (May 2005) at the intervention and control schools. Process questions regarding the implementation and appreciation of the intervention were included in the first follow-up questionnaires for children and parents.
  • Children were asked to complete the questionnaires during school hours in the presence of a project worker and took a questionnaire home to be completed by one of the parents
  • Teachers were asked to complete two questionnaires:
    • One half-way through the first intervention period
    • One at the end of the first intervention period.

Dietary Intake/Dietary Assessment Methodology

  • Frequency of children's usual fruit intake was assessed by one food frequency question: "How often do you usually eat fresh fruit?"
  • Frequency of children's usual vegetable intake was assessed by the sum of three food frequency questions: "How often do you usually eat salad or grated, raw and cooked vegetables?" Response options ranged from never (zero) to every day, more than twice per day (seven).


  • The curriculum consisted of 16 lessons guided by worksheets and a web-based computer-tailored feedback tool
    • Children completed this three times during the intervention period
    • Four of the lessons involved homework assignments
  • Parents were encouraged to be involved in the project through:
    • Homework assignments
    • Parental newsletters
    • A parent version of the web-based computer-tailored feedback tool
  • Fruits and vegetables were distributed to the schools; the method of distribution differed between the three countries:
    • In Norway and Spain, children were invited to subscribe (i.e., parents paid a fee) to an existing fruit and vegetable program and received a piece of fruit or a carrot during lunch or during a fruit break
    • In the Netherlands, all intervention children received a piece of fruit, a carrot or a tomato for free during a fruit break two school days per week.

 Statistical Analysis

  • Children with missing data or who over-reported fruit or vegetable intake (reported consuming more than 1,000g of fruit or vegetables in the previous day) were excluded from analysis
  • To assess potential drop-out bias:
    • Multiple logistic regression analysis was conducted with dropout as a dependent variable and country, gender, age, immigrant status, living circumstances, mother's educational level and child's intake at baseline as independent variables
    • Parents who did complete the process questions were compared to parents who completed the questionnaire but not the process questions
  • Exploratory analyses were first conducted to assess associations between changes in fruit and vegetable intake between baseline and follow-up and:
    • Different levels of the intervention characteristics
      • Degree of implementation of the school curriculum
      • Parental involvement
      • Child appreciation of the intervention
    • Gender
    • Country
    • Intake at baseline
  • Multi-level analyses with random intercepts were conducted in order to account for the nested design of the study:
    • Associations between the intervention characteristics (i.e., degree of implementation, parental involvement, child appreciation) and effects of intervention (i.e., change in fruit and vegetable intake between baseline and follow-up) were assessed
    • These analyses were adjusted for gender, country and baseline values for fruit and vegetable intake
    • Regression models with all intervention characteristics and without the parental involvement intervention characteristic were tested
    • All analyses were conducted with the total sample and separately for each country.
Data Collection Summary:

Timing of Measurements

  • Prior to the intervention (September 2003)
  • Immediately after the intervention (May 2004)
  • At the end of the following school year (May 2005). 

Dependent Variables

  • Children's frequency of fruit intake: Assessed by one food frequency question: "How often to you usually eat fruit?" with response options ranging from never (zero) to every day, more than twice per day (seven)
  • Children's frequency of vegetable intake: Assessed by three food frequency question: "How often to you usually eat salad or grated, raw and cooked vegetables?" with response options ranging from never (zero) to every day, more than twice per day (seven).

Independent Variables

Process measures for the intervention characteristics:

  • Degree of implementation of the school curriculum:
    • Represents both the quantity (dose delivered) and the quality (fidelity) of the school curriculum, assessed by asking teachers:
      • Whether they had implemented each lesson (yes or no)
      • Whether they had followed the instructions in the teacher's manual (yes, all of it; no, some of it; or no, not at all)
    • A composite score was calculated by summing the quantity and quality scores for each of the 16 activities
  • Parental involvement:
    • Assessed by asking parents:
      • Whether they had helped their children do the four homework assignments that specifically asked for their input  (yes or no)
      • Whether they had conducted the computer-tailored tool for adults  (yes or no)
      • Whether they had seen at least two of the three newsletters (yes or no)
      • Whether they talked about the project with their child (often, sometimes or no)
  • Children's appreciation of the intervention was assessed by asking children:
    • Whether they liked eight different project activities (e.g., the homework assignments, the computer-tailored test) (liked it a lot; liked it; did not like it)
    • Whether they liked the project in general  (liked it a lot; liked it; did not like it).

Control Variables

  • Gender
  • Age
  • Mother's educational level
  • Family characteristics
  • Immigrant status
  • Country
  • Fruit and vegetable intake at baseline. 
Description of Actual Data Sample:
  • Initial N: Total eligible sample was 1,115 children
  • Attrition (final N):  868 children (392 boys), 559 parents
  • Age: 10.7±0.54 years 
  • Ethnicity (country of origin):
    • Norway: 28%
    • Spain: 36.8%
    • The Netherlands: 35.2%
  • Other relevant demographics:
    • Living circumstances:
      • Live with both parents: 76.2%
      • Do not live with both parents: 23.8%
      • Live with two adults: 85.4%
      • Live in a single-parent family: 14.6%
    • Parental country of origin:
      • Both parents born in the country where the study was conducted: 73.1%
      • At least one parent born in a country other than where the study was conducted: 29.1%
    • Educational level of the mother, father or caretaker:
      • Less than 10 years: 31.8%
      • 10 or more years: 68.2%
  • Location: Norway, Spain and the Netherlands.
Summary of Results:

Adjusted Means* and 95% CIs of Frequency of Fruit and Vegetable Intake for Low, Medium and High Implementation and Appreciation of the School Curriculum and Parental Involvement: The Pro Children Study

Intervention Characteristic


N = Total Sample

 Adjusted Mean (Times per Day), (95% CI)


Appreciation (range, one to three)

Low (less than two) 


-0.13 (-0.23, -0.02)

Medium (two to 2.5)


0.00 (-0.10, 0.10) 

High (more than 2.5) 327

0.28 (0.18, 0.37)

School curriculum (range, zero to 16) Low (less than 7.5) 224 -0.02 (-0.13, 0.10)
Medium (7.5 to 10) 318 0.00 (-0.09, 0.09)
High (less than 10) 326

0.18 (0.08, 0.28)

Parental involvement (range, zero to seven)
Low (less than 2.5) 186 0.03 (-0.10, 0.15)
Medium (2.5 to four) 164 0.06 (-0.07, 0.20)
High (more than four) 209

0.19 (0.07, 0.31)

Appreciation (range, one to three)
Low (less than two) 256 -0.09 (-0.21, -0.02)
Medium (two to 2.5) 285 -0.02 (-0.13, -0.08)
High (more than 2.5) 327

0.37 (0.27, 0.48)

School Curriculum (range, zero to 16)
Low (less than 7.5) 224 -0.05 (-0.20, 0.06)
Medium (7.5 to 10) 318 0.12 (0.01, 0.23)
High (less than 10) 326

0.21 (0.09, 0.32)

Parental involvement (range, zero to seven) 
Low (less than 2.5) 186 -0.02 (-0.16, 0.11)
Medium (2.5 to four) 164 -0.03 (-0.17, 0.11)
High (more than four) 209

0.28 (0.15, 0.40)

*Adjusted for gender, country and intake at baseline.

Other Findings

  • Dropout:
    • Children from Norway (OR=0.36; 95% CI: 0.67 to 0.77) dropped out significantly less often than children from Spain and the Netherlands
  • Degree of intervention implementation:
    • The degree of implementation (number of lessons implemented) was significantly higher in Norway (P<0.01), compared with Spain and the Netherlands, and significantly lower in the Netherlands (P<0.01) than in Spain and Norway. All countries showed the same downward trend in the implementation of the school curriculum; all school teachers implemented the first two worksheets while the last worksheets were only implemented by one out of three teachers.
    • Mean scores for children's appreciation of the project were significantly higher in Norway compared with Spain and the Netherlands (P<0.01)
    • Parental involvement was significantly higher in Norway (P<0.05) and significantly lower in the Netherlands (P<0.05)
      • Parents of girls reported greater involvement than parents of boys (P<0.05)
      • Parental involvement was higher among children who lived with both parents (P<0.05) or with two adults (P<0.05) than among children who did not live with both parents or only lived with one adult
    • Degree of school curriculum implementation and intervention appreciation were not associated with gender, age of child, mother's educational level, family characteristics and immigrant status
  • Impact of intervention characteristics on children's fruit and vegetable intake:
    • Children's appreciation of the project and  degree of implementation of the school curriculum were significantly associated with changes in children's frequency of fruit intake
      • Children who scored highest on appreciation of the intervention had a significantly greater increase in fruit intake compared to children who scored medium (P<0.01) or low (P<0.01) on appreciation. There were no differences between the medium or low appreciation groups.
      • The strongest increase in fruit intake was found among children who completed more than 10 lessons at school compared to those who completed seven and 10 lessons  (P<0.05) or less than seven lessons  (P<0.05). There were no differences between the medium or low implementation groups.
      • Parental involvement did not have an effect on changes in children's frequency of fruit intake
    • Children's appreciation of the project, degree of implementation of the school curriculum and parental involvement were significantly associated with changes in children's frequency of fruit intake
      • Children who scored highest on appreciation of the intervention had a significantly greater increase in vegetable intake compared to children who scored medium (P<0.01) or low (P<0.01) on appreciation. There were no differences between the medium or low appreciation groups.
      • The strongest increase in vegetable intake was found among children who completed more than 10 lessons at school compared to those who completed less than seven lessons (P<0.01). No difference was found between medium and high degree of implementation, but the increase was stronger for children who experienced a medium compared to a low degree of implementation  (P<0.05).
      • Children with the highest parental involvement showed the highest increase in vegetable intake compared to children who score medium (P<0.05) or low (P<0.01) on parental involvement. No differences were found between medium and low involvement.
    • Data on adjusted means of frequency of fruit and vegetable intake, including and country-specific analyses, confirmed the above results.


Author Conclusion:
  • The results from this study demonstrate that the degree of implementation and children's appreciation of the Pro Children intervention are associated with greater increases in children's fruit and vegetable intakes
  • Parent involvement in the intervention was low and children were the least enthusiastic about homework assignments that had to be carried out with one of their parents.


Reviewer Comments:

Strengths and limitations as noted by authors:

  • Strengths:
    • An  important strength of this study is that the intervention was tested in three very different geographical and cultural settings
    • Validated instruments were used to assess intake
  • Limitations:
    • The dropout analyses among parents revealed that a selective group of parents completed the first follow-up questionnaire; parents from families in which at least one parent was born in a country other than the research country and parents from families in which both the parents of the child no longer live together were more likely to drop out. Results presented might therefore not be fully representative, especially for the Dutch sample where the participation rate was lowest.
    • The validity and reliability of the assessment of the four intervention characteristics has not been tested. Teachers could have given socially desirable answers and over-estimated the implementation. A validation study comparing three different methods  (i.e., classroom observations, teacher self-reports and post-implementation interviews) to assess implementation of a school-based health curriculum showed that different methods lead to different implementations rates.
    • As in a site study, implementation rates based on teachers’ self-reports were higher, suggesting that over-estimation of implementation might also have been the case in our study for which we used teachers’ self-reports
    • Authors note that observations, questionnaires and interviews are a common combination to assess implementation. But they mainly used questionnaires in which detailed data were collected, while logbooks were used to complete missing data. Relying on only one data source, however, might reveal less reliable measures. Extensive interviewing of the teachers immediately after the intervention period or dual observations of fidelity might have been more valid than self-reports.
    • Another limitation of this study is the lack of ability to state causality. When assessing associations between process measures and changes in intake, it might also be that children who already eat more fruit and vegetables, or who like fruit and vegetables better, appreciate the project more or are more active in stimulating their parents to conduct activities with them. However, this study does help to shed some light on how the Pro Children intervention changed effects on intake of fruit and vegetables.

Research Design and Implementation Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to nutrition or dietetics practice?
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies)
Validity Questions
1. Was the research question clearly stated?
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated?
  1.3. Were the target population and setting specified?
2. Was the selection of study subjects/patients free from bias?
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?
  2.2. Were criteria applied equally to all study groups?
  2.3. Were health, demographics, and other characteristics of subjects described?
  2.4. Were the subjects/patients a representative sample of the relevant population?
3. Were study groups comparable?
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?
  3.3. Were concurrent controls used? (Concurrent preferred over historical controls.)
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?
  3.5. If case control or cross-sectional study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable. Criterion may not be applicable in some cross-sectional studies.)
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?
4. Was method of handling withdrawals described?
  4.1. Were follow-up methods described and the same for all groups?
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for?
  4.4. Were reasons for withdrawals similar across groups?
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study?
5. Was blinding used to prevent introduction of bias?
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status?
  5.5. In diagnostic study, were test results blinded to patient history and other test results?
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described?
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied?
  6.2. In observational study, were interventions, study settings, and clinicians/provider described?
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured?
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described?
  6.6. Were extra or unplanned treatments described?
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?
  6.8. In diagnostic study, were details of test administration and replication sufficient?
7. Were outcomes clearly defined and the measurements valid and reliable?
  7.1. Were primary and secondary endpoints described and relevant to the question?
  7.2. Were nutrition measures appropriate to question and outcomes of concern?
  7.3. Was the period of follow-up long enough for important outcome(s) to occur?
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?
  7.5. Was the measurement of effect at an appropriate level of precision?
  7.6. Were other factors accounted for (measured) that could affect outcomes?
  7.7. Were the measurements conducted consistently across groups?
8. Was the statistical analysis appropriate for the study design and type of outcome indicators?
  8.1. Were statistical analyses adequately described and the results reported appropriately?
  8.2. Were correct statistical tests used and assumptions of test not violated?
  8.3. Were statistics reported with levels of significance and/or confidence intervals?
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?
  8.6. Was clinical significance as well as statistical significance reported?
  8.7. If negative findings, was a power calculation reported to address type 2 error?
9. Are conclusions supported by results with biases and limitations taken into consideration?
  9.1. Is there a discussion of findings?
  9.2. Are biases and study limitations identified and discussed?
10. Is bias due to study’s funding or sponsorship unlikely?
  10.1. Were sources of funding and investigators’ affiliations described?
  10.2. Was the study free from apparent conflict of interest?