This qualitative case study examined the ability of kindergarten through grade five classroom teachers in one school district to diagnose computational error patterns and be prescriptive with instruction and intervention based on the computational error pattern. This study extends the work of Ashlock (2006) and Riccomini (2005) by presenting both addition and subtraction computational error patterns for teachers to analyze. Through the use of a survey instrument developed by the researcher which was based on the previous work of Ashlock (2006) and Riccomini (2005), teachers responded to open-ended questions to identify the type of error made as well as to state recommendations for instruction and intervention. As in the work of Ashlock (2006) and Riccomini (2005) the classroom teachers were most often able to diagnose the type of computational error, but the recommendations made by this sample of teachers did not align with the recommendations made by Ashlock(2006) and Riccomini (2005). This finding parallels the results of Ashlock (2006) and Riccomini's (2005) work. Through the use of interviews, this study also obtained data regarding the teaching strategies used by teachers of kindergarten through grade five in one school district for developing numeracy in young students. It looked at teachers' understanding of the relative importance of developing numeracy in young students, the role it plays in student success, and how the mathematics practices are related to teaching strategies for teaching mathematics. Then, by utilizing a gap analysis, professional development needs for this sample of teachers in the area of mathematics pedagogy were defined.