Suwanwong, S.; Yamsang, W. .; Yamsang, N. Diagnosis of Mathematical Defects in Addition, Subtraction, Multiplication, and Division of Prathom Sueksa Four Students at Schools in the Service Area of Chang Khwa Subdistrict Municipality, Kanchanadit District, Suratthani Province. jmhs1_s 2021, 4, 982-998.