This paper is based on a study which sought to examine the various errors and misconceptions committed by students in algebra with the view to exposing the nature and origin of the errors and misconceptions in secondary schools in Machakos district. Teachers' knowledge on students' errors was investigated together with strategies for remedial teaching. Descriptive survey design was adopted on four hundred and thirty form two students and fifteen mathematics teachers. Data was analyzed using descriptive statistics. The findings indicate that students make errors and that they have misconceptions in algebra. In this paper some students' misconceived notions and the root causes of these misconceptions are shared. Opportunities afforded by these feedbacks for instruction of mathematics are also shared. The study posits that teachers' use of student's mathematical ideas when purposely engaged can support teacher student interaction in mathematics classrooms. However, most of the teachers hardly made use of the students' mathematical ideas and this lead to instructional strategies that did not address students' difficulties. So to enhance teachers' use of students' experiences, teacher education will need to focus on encouraging a variety of ways of teacher-student interaction during which students' mathematical ideas should be considered exhaustively.