One hundred and sixty-two children aged 9–16 years from Southern Ontario, Canada participated in the study. Subjects were recruited from numerous schools and sports clubs. As this project is part of a larger study, only male subjects were recruited at this point. All testing was approved by the Brock University Research Ethics Board. Informed written consent was obtained from both the subjects and their parents/guardians prior to their involvement with the study. Subjects were divided into one hundred and seven (107) elementary school (ES, 9–12 years, mean age 11.2 ± 0.7 years) and fifty-five (55) high school (HS, 14–16 years, mean age 15.4 ± 0.5 years) groups. These two groups were selected to represent two different levels of pubertal maturity. Indeed, pubertal maturity, as self-assessed using secondary sexual characteristics [15, 16], was lower in ES (Tanner stages 1–2) as compared with HS (Tanner stages 4–5). Body weight was measured using a calibrated Zenith digital scale. Height was measured with an Ellard Instrumentation board length statiometer (Monroe, WA, U.S.A). Relative body fat was estimated from skinfold thicknesses of the triceps and subscapular landmarks . As expected, the groups were significantly (p < 0.05) different in terms of physical characteristics with ES boys being smaller in size (41.2 ± 10.2 kg, 146.6 ± 7.8 cm) than HS (65.3 ± 11.1 kg, 172.6 ± 7.0 cm). Both groups had a relatively small percentage of boys that were overweight (23% and 13% for ES and HS, respectively) with no significant differences in relative body fat between groups (19.3% and 16.4% body fat for ES and HS, respectively). Additionally, no boys that were classified as obese were used in the analysis of this study.
Each subject attended a nutritional interview in a private room. The 20- to 30-minute interview included the calcium RAM  and a 24-hour dietary recall. Both questionnaires were administered using visuals aids to approximate the serving sizes of various foods. Subjects report was taken independent of parental response, as parents have been found to not be reliable reporters of their children's food intake out-of-home . All interviews were conducted by the same trained and experienced researcher.
The RAM includes 30 items and refers to a typical day [see Additional file 1]. Two categories were added to the original RAM questionnaire, namely calcium enriched orange juice and specific nutritional supplements. The calcium values (mg) for nutritional supplements and calcium enriched orange juice were obtained through the Diet Analysis 6.0 program (Belmont, CA, U.S.A).
For the 24-hour dietary recall, subjects were asked to recall everything consumed (including foods, beverages, sauces and condiments) the day prior to the interview. Prior to answering the 24-hour dietary recall, subjects were asked if the last 24 hours were typical for their diet. If it was not a typical day (e.g. birthday party, family gathering, eating out), they reported two days prior to the interview date. The 24-hour dietary recall started from the first meal or beverage consumed at waking until midnight of the reporting day. The data were analyzed using the Diet Analysis 6.0 program for total energy intake, and total calcium intake. When nutritional information was not available through the software program, manufacturer's labels and information from fast food chains were utilized.
Intra-class correlation was used for the comparison between the RAM and the 24-hour recall method. A one-way ANOVA was used to determine differences in anthropometric variables between groups. A paired t-test was used to compare the mean daily calcium intake obtained by RAM with that calculated based on the 24-hour dietary recall. To examine age differences in the validity of RAM, an ANOVA for repeated measures, with age-group (ES vs. HS) being the between-subject factor and assessment method (RAM vs. 24-hour) being the within-subject factor, was also performed. All data are expressed as mean ± SD. Statistical significance was accepted at p ≤ 0.05.