Hello Harsh,

Both 10th and 12th class matters. When student is in 10th then also it matters to score good marks and when student is in 12th than also it matters a lot. After 12th both 10th and 12th results are required in every field. One should always work hard in these two classes. Though 12th matters the most because our future depends on that class result. 

If you score good marks you will get good college good placement and than good job. So work hard. 

All the best.