This study compared the differences in the Criterion-Referenced Competency Test (CRCT) mathematics and science achievement scores of boys and girls in Grade 7 at two urban middle schools. The data allowed the researcher to determine to what degree boys and girls in Grade 7 differ in their mathematics and science achievements within a single-gender environment versus a coeducational learning environment. The study compared any differences between boys and girls in Grade 7 within a single-gender environment in the subjects of mathematics and science, as measured by the CRCT assessments. The study also compared differences between boys and girls in Grade 7 within a coeducational environment in the subjects of mathematics and science, as measured by the CRCT assessments. Two middle schools were used within the study. One middle school was identified as a single-gender school (Middle School A); the other was identified as a coeducational school (Middle School B). This quantitative study applied the use of a descriptive research design. In addition, CRCT scores for the subjects of mathematics and science were taken during the spring of 2008 from both middle schools. Data were measured using descriptive statistics and independent t test calculations. The frequency statistics proceeded to compare each sample performance levels. The data were described in means, standard deviations, standard error means, frequency, and percentages. This method provided an excellent description of a sample scored on the spring 2008 CRCT mathematics and science assessments.