Question

重要的不是你在考试中得了几分，而是你是否努力学习了

翻译为什么是
what doesn"t matter is not what score you have got but whether you studied hard
为什么是doesn"t而不是what mattered?

Answer 1

之前说的有点问题，这句子是what doesnt matter 作表语从句，不是主语从句，但不管怎么样都不是what作主语。colefafa同学建议你深造一下高中英语。你的“what一般不用于陈述句子开头”恐怕连初中英语的水准都不及。还有你的句子很明显语法有错么~It is how hard you study that matters rather than how many scores you get. (请注意动词)

我觉得这句子应该是what matters，不是what doesnt matter，写的人错了。另外还有个语法错误，but whether you HAVE studied hard.最简单的道理，两个并列的短句，怎么能一个有have, 一个没有。
what mattered用过去式有点怪，如果没有语境的话~如果一定要用过去式，那么应该说what mattered was not what score you had got, but whether you had studied hard,后面全部得用过去式或者过去完成时。

Answer 2

这不是正确的用法，你应该说 it is how hard you study that matter rather than how many scores you got
what 一般不用于陈述句子的开头。
那位朋友你不要误人子弟了！那个句子根本就是错误的。

Answer 3

no matter how many scores you got, if you've been trying hard.