Student gender and teaching methods as sources of variability in children's computational arithmetic performance.

An experimental study of the effects of a didactic teaching approach and a constructivist teaching approach on 3rd- and 5th-grade boys' and girls' performance on arithmetic computation problems was conducted. Two groups of children, matched on the basis of initial computation performance as well as grade and gender, were taught how to solve arithmetic problems using one of these two instructional approaches. Analysis of subsequent computation test performance revealed that 5th graders scored higher than 3rd graders, and there was a significant interaction between gender and instruction group. After instruction, girls in the didactic group outperformed boys in both instruction groups and girls who had been taught using constructivist approaches. Gender differences in computation performance can appear relatively early, by 3rd grade, if didactic instruction strategies are used to teach computational rules. The pattern of gender differences suggests that didactic teaching does not handicap boys. Rather, it appears that didactic instruction enhances computational performance in girls.

Illegitimate recombination in Bacillus subtilis: a site-specific mechanism in the formation of plasmid pKBT1.

The Bacillus subtilis plasmid pKBT1, the product of in vivo recE4-independent recombinal events, contains segments derived from pUB110 and the B. subtilis chromosome. To determine whether the pUB110 sequence is intact in PKBT1, two 1 kb fragments, each containing a site at which chromosomal and pUB110 sequences are joined, were cloned and sequenced. Sequencing data revealed that: 1). An intact copy of pUB110 is present in pKBT1; 2) The apparent recombination sites were adjacent to the Bam HI-generated ends of pUB110 sequences; 3) pTL12-derived sequences from the original transforming DNA were limited to no more than 1 bp outside the Bgl II recognition sequence; 4) Recombination sites at both ends of pUB110 contain a 19 bp inverted repeat with 15 homologous nucleotides. These findings suggest a site-specific mechanism acting during in vivo formation of pKBT1.