The purpose of the study was to determine the effects of type of grouping (multibase (M) or base ten (T) ) and the time that base representations are introduced (initially (EB) or after counting, reading and writing numerals (LB) ) on achievement in numeration in grade one. Four intact classes of 110 students participated, and a 2 x 2 factorial design was used. Achievement measures were developed by the investigator. Results showed no significant differences between M and T; low-ability pupils achieved better in T throughout. After the posttest, LB had consistently higher means and adjusted means than EB, and had significantly more students with mastery on the retention test. (Author/DT)