I’ve asked something like this before, and I got an answer, but I’m still confused about the whole classes taken out of sequence thing. I understand if one were to take some class (lets say Philosophy 20B) and then take the Intro class (PHIL 1) they won’t get the credit, correct? I wholly know that, if I were to take Philosophy 20B and then try to take 20A out of sequence, I will not get credit for 20A.
Does the numbering of classes really matter as long as classes aren’t completely related? Or, what are the conditions under which one wouldn’t get credit for taking courses in/out of sequence? I’m taking Philosophy 20B (modern european phil), and I want to take PHIL 10 (logic), 17 (Buddhism), etc. Would I be fine, or am I disallowed from taking anything lower than 20B because I jumped to that? I’m probably completely understanding it incorrectly, but I just want to clarify for planning my classes next semester.
tldr: When does improper sequence come into play? Do course numbers matter, or does one just have to follow the specific A, B, C, etc. sequence?
@lindyk8 seems to have got this down. I’ll defer to her good judgement 
I think it has to do with sequences in classes, esp math and sciences. Humanities might be in the clear, since they aren’t sequential. I.e Math A/B/C need to be taken in order, but Psych 2 can come after Psych 6, etc.
Taking classes above and below numbering is fine as long as they aren’t related (phil 1a, 1b, etc) unless you are taking a course that was a pre-req of a course you already took. (Ex: let’s say Engl 110 is a pre-req of Engl 1111, and if for some reason you got into 111 without 110, you would not be able to go back and take Engl 110. Well, you can, but you won’t get credit.)
But in terms of just disparate classes, you can take in any order.
It really depends on the class. For example, I took Econ 1B then Econ 1A since microeconomics and macroeconomics are related but not considered a sequence. The same goes for philosophy. The courses you want to take are not a sequence. Usually, if the class is a prerequisite for another class, then they’re a sequence.
Spencey is correct. Not all matter. But most do. That’s why they’re numbered that way. I would always be super careful when assessing sequencing of a b c, etc as that is the leading cause of students losing units or missing major prep. But he is right. Not all will be required to be a sequence.
And for instance, in terms of IGETC, taking critical thinking (English 102) ahead of English 100 comp will lead to partial IGETC as their sequencing is off, because 100 was a pre-req. So, yeah the course numbers won’t always tell the story. Pre-reqs are key.
So… Here is my situation. My college has English 1A (comp), English 1B(Critical Thinking), and for international students, there is ESLL 26.
Pre-reqs for English 1A are ESLL 26 or enough placement test score, and pre-reqs for English 1B are ESLL 26 or English 1A.
So… for international students who finished ESLL 26, they can take English 1B first, and then take English 1A. I have seen several friends who have done this way, and I also did like that.
Because 1A and 1B have the same pre-req, ESLL 26, I thought that they are somehow equivalent. Will this also lead to partial IGETC? Since IGETC is very crucial for the application, I feel like I am doomed 
Talk to a UC. I watched a UC seminar in which the person only got partial IGETC by going out of sequence. It may be OK, but be sure to verify from both sides.
I’m not quite sure why you can’t take 1a first.
@lindyk8 Actually, I tried to take both of them, English 1A and 1B, in the same quarter, but my English 1A class was cancelled because of the professor’s health problem. So, I didn’t have any choice but taking English 1B first, then taking 1A next quarter.
Oh, I see. Well, IGETC certification is at the sole discretion of the CCC. So if they sign off, the UC honors it. I guess that is the key, and you seem to say they’ve done that in the past. In the example I noted, the CCC would not sign off on full IGETC as courses were out of sequence.