Here are my suggestions:
"Shock and denial is what most students experience when their writing assignments are marked and handed back with a low grade. They usually receive a low grade because of a simple reason:
they write poorly. Most would assume that their low grades are caused by their own lack of responsibility,
such as not paying attention in class or not doing homework. However (Remove comma)
they would assume wrong. Schools are the one to blame, or to be more specific, the people who planned the school's
English curriculum. Like a driving teacher who does not
teach his students anything and expects his students to be able to pass their driving tests, in the curriculum (Remove comma)
students are not taught how to write well while being expected to do well on writing tests and assignments. Since schools do not
teach students how to write well, what students could do then is to teach themselves how to write well because writing well is an important skill."
Nice work. Some mechanical errors, but you've got a good opening statement here. When you finish the second paragraph, go ahead and post it and we can work on that as well.