Are my sentences correct?

First things first: Do the following sentences sound natural to you? Sentences is a plural noun, and therefore takes a plural form of the verb.

As you ask whether the sentences sound natural, I will render them into the commonly used forms (of American English).

There's a student in the class (or "our class") called Jack. Nobody likes him but his classmate Micheal. Somebody had* stolen the teacher's (you don't need to repeat "the class" because that will be understood) wallet, and the rest of the class know ("class," although singular, represents several individuals, and is understood to be a plural noun) who did it. Despite the fact, they backed up the true culprit, and blamed Jack.

(*I wrote "had stolen" because this passage describes something which happened in the past--the unjust accusation of Jack, Michael's defense of him and the mother's comment to the Principal (Headmaster). Therefore, the theft is from the past, but an earlier past, an anterior past. "Had stolen" is the anterior past form of the verb, indicating that the theft took place before the the accusation and the defense of Jack.)

Michael was the only one sticking up for Jack before the class, (all the class sounds awkward, and is understood in context without specifying all of the class) saying it wasn't him who had stolen the teacher's wallet. I don't believe he did it.

In British usage, one would say the Headmaster. In American usage, one would say the Principal. Any other differences between American and British usage will doubtlessly be pointed out by a British member here, if any show up.

There's a student in our class called Jack. Nobody likes him but his classmate Micheal. Somebody had stolen the teacher's wallet, and the rest of the class know who did it. Despite the fact, they backed up the true culprit, and blamed Jack.

Micheal was the only one sticking up for Jack before the class, saying it wasn't him who had stolen the teacher's wallet. I don't believe he did it.

Terms like headmaster and headmistress have fallen out of favour, headteacher tends to be used now. It makes life easier if all you know about the head is their surname and initials.

Over here principals are in charge of colleges.

This could momentarily confuse 'cuz it seems to say the class itself is named 'Jack', where it was taught how to raise heavy objects

In one of the classes there's a student called Jack, despised by all the rest of his classmates except Michael

Somebody had stolen the teacher's wallet, while the rest of the class is sure Michael did it. Nevertheless they backed up the true culprit but for some reason tried to put the blame on Jack

Remarkably enough, since Michael was the only one sticking up for Jack, continuing to defend him, I don't believe he was guilty either

Ignore Dale, he's in the early stages of Alzheimer's and doesn't really know what he's talking about.

Most folk do anyway

Actually pretty late, Iz, don't 'mem' what I did five minutes ago

doesn't really know what he's talking aboutTo some extent, Push, I'm sure you're right. But if I can clarify my remarks in any to improve your grasp, please respond

I'm not being nasty. You're an unreliable source, and people, especially people learning English, need to know that.

Okay Iz, I'm sure you're right, but if you could give me a 'zampl,' a link of some sort, or even fwd a sentence or two, I'd be most happy to clarify

Perfect! You're great, Setanta

I hope that helped. I'd be glad if it did.

You admit your sentences may need clarifying, that in itself should tell you to keep off the language threads.

Why not join the debate on confederate statues?

Alas yew Iz, I've entertained that very observation. But it's a compulsion. Out of a couple hundred such attempt, I actually was awarded one 'best'

Bores me to death, but thanks Iz anyhow

So Iz where and in what way
Links welcome

Dale, I will test you. Do you see anything wrong with the following sentence?

You admit your sentences may need clarifying, that in itself should tell you to keep off the language threads.

Do you think a semicolon instead of a comma?

Iz at 86 w/Alzie's, I'm somewhat confused by that last'n'. I had offered to clarify any specific sentence or even para with which to you or other had proved unsatisfying, if you'd send a link. I'm not sure, but I think that means searching for a typical example of my incompetent fumbling,, highlighting it, copying, then placing in a new posting as a response, indicating below it, eg, what was found to be inadequate

I know your situation which is why I think you should lay off the language threads.

I will repeat the offer I made about giving a considered response to all your posts if you lay off the language threads, although not until I get back from Copenhagen.

Heck Izzy have a good time

Pretty good so far.