Desperately need help

Dear teachers,
I am from a non-English speaking country, and need help to see whether the following sentences which I constructed are correct.
1. If students fail to pay the outstanding fees, they are required to continue in the Elementary class and $2,000 will be imposed.
2. Students who did not achieve minimum of 75 % attendance will be barred from sitting for the examination.
Note : For sentence 2 , will it be correct if we do away with "for " . Can I just write like this : Students who did not achieve minimum of 75 % attendance will be barred from sitting the examination.
3. Attached is a copy of the final examination question paper for our Elementary students. I have to read through again the question paper as to ensure that there are no typo or lexical errors.
Thanks and I really appreciate teachers' help.

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1. If students fail to pay outstanding fees, they are required to continue in the Elementary class and [a fine of? additional tuition of?] $2,000 will be imposed.

2. Students who did not achieve a minimum of 75% attendance will be barred from sitting (for) the examination. (Without the 'for' is very BrE). I don't think that 'bar' is the most common verb; 'not be allowed/permitted to sit' may be more usual.

3. Attached is a copy of the final examination question paper for our Elementary students. It has not yet been proofread.
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