Summary.1.—The extent of fluctuation generally characteristic of a mixed group of pre‐adolescents and adolescents was significantly greater than that of pre‐scholarship primary children, particularly in Arithmetic. Of all tests, one of Food Aversions showed most extensive evidence of fluctuation.2.—The difference between the average group index of fluctuation in cognitive and in non‐cognitive tests was significant at the 1 per cent. level whereas with the younger groups it had been either insignificant or significant only at the 5 per cent. level.3.—The size of the group indices of fluctuation for all ten pairs of testing occasions was in phase neither between functions and within groups, nor within functions and between groups.4.—No general factor was observed in the inter‐correlations between individual indices of fluctuation on all six functions.5.—Further investigation will be necessary before conclusions can be drawn about the effect of the sex factor on contributions to fluctuation in performance during pre‐adolesce