['To assess the validity of the Food Intake Recording Software System (FIRSSt) against observation of school lunch and a 24-hour dietary recall (24hDR); and to test the effects of sequencing, observation and a hair sample as a bogus pipeline on accuracy of dietary report.', 'Six-group design systematically varying sequence of self-report (FIRSSt vs 24hDR), observation of school lunch and hair sample as a bogus pipeline manipulation, with random assignment of participants.', '138 fourth-grade students in 2 elementary schools.', 'Accuracy of reported food consumption was measured in terms of matches, intrusions, and omissions among the FIRSSt, 24hDR, and as observed at school lunch. Students also completed self-report of performance with FIRSSt.', 't tests, Pearson correlations, analysis of variance, factor analysis.', 'When compared with school lunch observation for one meal, FIRSSt attained 46% match, 24% intrusion and 30% omission rates, while a dietitian-conducted 24hDR obtained 59% match, 17% intrusion, and 24% omission rates. FIRSSt attained 60% match, 15% intrusion, and 24% omission rates against 24hDR for all meals in the previous day. There was no evidence of sequence of assessment affecting accuracy indicators, but there was a weak effect of school lunch observation on percent intrusions. Obtaining a hair sample reduced the omission rate for FIRSSt vs 24hDR and increased the match rate for 24hDR vs observation, thereby enhancing this as a bogus pipeline procedure. Children generally enjoyed completing FIRSSt. Hispanic children were more likely to report problems using FIRSSt.'] Is the food intake recording software system valid among fourth-grade children?