This article is a synthesis of unpublished and published experiments showing that elementary memory scores (words and pictures immediate recall; delayed recall, recognition), which are very sensitive to aging and in pharmacological protocols, have little or no correlation with school achievement. The alternative assumption developed is that school achievement strongly depends on the long-term memory of scholastic knowledge (history, literature, sciences, maths, etc), called encyclopedic memory. a A longitudinal study from the grade 6 to the grade 9 of a cohort of eight classes of a French college, was undertaken in order to observe the implication of the encyclopedic vocabulary (i.e. Julius Caesar, Manhattan, Shangaï, Uranus, vector) in school performance. An inventory in the school textbooks gives approximately 6000 encyclopedic words in grade 6 to 24000 in grade 9. The encyclopedic storage capacity was estimated at the end of each year by a multiple-choice questionnaire with random samples of words (800 items; 8 subjects). The results show an estimation of 2500 words acquired at the end of grade 6, to 17000 at the end of grade 9. The correlations range from 0.61 to 0.72 between the score of encyclopedic memory and the average school grades.