The colon that is used in this sentence is extraneous. While the part of the sentence that precedes the colon is an independent clause, the part of the sentence that follows the colon is not; it is a subordinating clause because it is introduced by "since," which is here acting as a subordinating conjunction. Colons are not used to separate independent and subordinating clauses.

You may use a colon before a list or an explanation, as long as the preceding clause is able to stand on its own. As such, the colon in the sentence above is incorrect and should be deleted. The colon in the example sentence comes in the middle of a clause, and thus is obviously incorrect.

You may use a colon before a list or an explanation, as long as the preceding clause is able to stand on its own (an independent clause, in other words). As such, the sentence above is correct as written. As a rule of thumb, you should not use a colon if you could not put a period in its place, delete everything after it, and still have a full sentence.

Punctuation is the issue here. A colon is used to introduce a list, which it does not do here. The appropriate punctuation to use here would be a semicolon, which is used to separate two independent clauses (such as these).

In this sentence, the colon is placed after want, in the middle of a clause. Colons should come after an independent clause, never in the middle of a dependent or independent clause.

Here, no colon is necessary. Although the sentence is presenting a list, the part preceding the list is not a complete sentence, so the colon should not be used.

Colons may be used to separate clauses in sentences, but only where you would also be able to use a period. You cannot use a period in the place of the colon in the sentence above, so that colon is erroneous. The sentence should read, "When you behave this badly in class, it reflects poorly on the entire school."

Colons are used prior to lists of things in sentences, rather than semi-colons; therefore, the semi-colon in the sentence above is erroneous. The sentence should read, "To complete their final projects, all students must prepare the following: a presentation, a posterboard, and a paper."

Colons may be used prior to lists of things in sentences; however, this is only the case if there are three or more items in the list. As the list in the sentence above has only two items (the movies and the park), the colon above is erroneous. The sentence should read, "I'd like to take you to the movies or the park today."

Colons serve primarily two purposes. The first is to precede a list in a sentence, and the second is to join two independent clauses of a sentence, as long as the second clause explains or expands on the first clause. For the second purpose, however, you may only use a colon where a period might otherwise be used, after an independent clause, and before a second independent clause that explains, or directly expands on the first clause. The colon in the above sentence is incorrectly placed. The best way to correct the sentence above is:

"Stop being to rude to Tommy: he is a very nice young man."