There is no necessity of going to school for getting the qualifications. You can appear 10th examinations, Intermediate examinations and degree examinations also as a private candidate. Without any prior qualification, you can directly appear for the degree examinations through open universities. For this, you have to get qualified for the entrance test. Many students who are studying in private unrecognised schools are considered to be private candidates only.
My mother's sister did her 12th class and then BA privately. She has not joined any school or college. She appeared as a private candidate. Then she did her MA and PhD by taking admission into the college and then university.