This paper explores misconceptions and errors (M/Es) of eighth-grade students in Nepal with a quasi-experimental design with nonequivalent control and experimental groups. The treatment was implemented with teaching episodes based on different remedial strategies of addressing students' M/Es. Students of control groups were taught under conventional teaching-learning method, whereas experimental groups were treated with a guided method to treat with misconceptions and errors. The effectiveness of treatment was tested at the end of the intervention. The results showed that the new guided treatment approach was found to be significant to address students' M/Es. Consequently, the students of experimental groups made significant progress in dealing with M/Es in mathematical problem-solving at conceptual, procedural, and application levels.