Tang there’s a slight difference in meaning.
There is no difference in meaning, Dale. But to understand that you first have to understand what reported speech is. The term certainly isn't particularly colloquial - it's a grammar term, but the use of reported speech is very colloquial, though that hardly means that it is limited to speech.
Here's an example of reported speech, me reporting your speech;
Dale told MsTan that there is/was a slight difference in meaning.
You do reported speech every time you tell someone what someone else said.
"My teacher said that we had to study hard.” could imply that over a period of time we had to do so in order to meet some sort of goal
That's not an accurate description when it is reported speech. In reported speech we use the past tense form of a verb not to signal an actual/real past situation, but rather, it simply is a signal that we are giving our description of what we believe the person said. We are telling the listener that this is reported speech, not an actual direct quotation.
Dale: By the way not sure what you mean by “reported speech” as it isn't colloquial.
MsTan [to jtt]: What did Dale say, JTT?
jtt: He said, and I quote, "By the way not sure what you mean by “reported speech” as it isn't colloquial." [Direct quotation]
jtt: He said that he wasn't/isn't sure what you mean by “reported speech” 'cause it isn't colloquial. [Reported Speech]
but maybe now any progress achieved back then means that today we might slack off a bit[/quote]