You can apply for the course as you have studies mathematics in first semester in BCA. There is no harm in applying, just go for it, fill in the application form and apply. Wait for the response/reply. If you are called, appear for the entrance examination select mathematics and any other subject, if you have taken languages(Hindi/ tamil/ telugu/ sanskrtit/ kannada) or English. Since you have to choose two subjects for teaching . There are many options for BCA. B.Ed degree is not essential for teaching computer science in schools. You can also choose to become a computer teacher in schools and teach children computer application/ computer science. You can directly approach the school and handover the application or apply online. If you are keenly interested in teaching mathematics then B.Ed degree is required to teach in schools and M.Sc in colleges. You can choose to pursue MCA/ MSC and find jobs in corporate sectors/ I T departments or as teaching faculty in colleges and schools. Depending on you personal situation and interests choose the right best choice and finalize.