Standard disclaimer: I'll often speak of foreshadowing, but that doesn't mean I'm at all committing to the idea that there was some fixed design from the word go -- it's a short hand for talking about the resonances that end up in the text as it unspools.
Standard spoiler warning: The notes are written for folks who have seen all of BtVS and AtVS. If they become relevant I'll spoil through the comics as well. Basically -- if you are a spoiler-phobe and haven't seen or read it all, read further at your own risk.
Teacher’s Pet, In Which Xander is Seduced by a Praying Mantis.
Xander’s turn to take the spotlight. We discover that Xander's nerdy bumbling exterior belies his inner bravery. We learn the answer to three questions in this episode:
What Buffy wants: The episode opens on Xander’s dream about rescuing Buffy. The episode ends with Buffy rescuing Xander. Buffy doesn’t want or need to be rescued by Xander.
But Buffy does want to be rescued by a man. This is the episode where the short-lived biology teacher reaches out to her in a supportive way. It means so much to her that she cries when he dies, and sentimentally tucks his glasses away at the end. Buffy wants a father figure. We’ll see this explicitly in Nightmares.
Strudel drops a footnote: On a minor, random note, re-reading the transcript where Dr. Gregory challenges her to do better, I could very easily give his lines to Prof. Walsh. In both cases Buffy responds well to these blunt challenges to live up to her potential. And, per usual for our hero, both of these would-be mentors get killed.
As a nice touch in this episode, anyway, we see that Dr. Gregory's imploring helped. Buffy did do her homework and learned that bats eat praying mantises. Whatever Buffy's challenges in the classroom, she is very good at weaponizing her knowledge, in this case using the bat sonar sound to disable the She-Mantis. She then figures out how to use the Fork Demon as a homing beacon, and, voila! she saves the day. Smart girl, that one.
Buffy wants to be taken care of by a man. Angel sees she’s cold and gives her his coat. She loves this. She’s into him. He’s still carefully reeling her in, giving her just enough to hook her, but not one jot more. He’s all smirky. She sighs. What Buffy appears to not notice is that Angel got thrashed by the fork vampire, who Buffy totally owned. One of the first things we’re being told about Buffy/Angel is that there’s a large gap between what Buffy sees in Angel (a mysterious protective figure) and what Angel is (a seducer who has said he’s too afraid to fight and who isn’t nearly as strong as Buffy).
Bottom line: Buffy wants a man she can look up to. Bear this in mind when she never quite falls for Spike. The fact that Buffy finally makes a move on Xander in season 8 is interesting in this regard. Cause as much as Buffy comes to respect and value him, Xander is not the guy she looks up to. The comics tell us, then, that being someone Buffy can look up to is no longer a non-negotiable requirement (making me all the more interested in what’s going to develop next in the Twuffy saga).
How Xander compares to Angel: Angel may be mysterious and have a cool coat; but Xander is still the real deal. Here we see this in the Blaine/Xander rivalry with Blaine (sexy exterior, cowardly interior) standing in for Angel. Xander is much less suave than Blaine, but much cooler under pressure. Indeed, he gets props for how he handles himself in the lair of praying mantis lady.
Strudel points out: we see Xander's jealousy of Angel cropping up here. He watches Angel's seduction of Buffy and notes the fact that Buffy failed to mention how big and good-looking Angel is. Interestingly, when he's explaining why the praying mantis lady picked him out, he jokes, "I wonder what she sees in me? It's probably the quiet good looks coupled with a certain smoky magnetism." He's almost describing Angel.
What Sex is: Really dangerous!!
Since this is Xander's first starring turn, it's worth taking a closer look at the introduction ("In Which Xander Dreams Large, and Drools in Reality..."). What he dreams is that he gets to play the typical strong male, saving the helpless female. In case there was any lingering doubt, this unsubtle exposition of his gender-based insecurity demonstrates that Xander is in truth under no illusions about his supposed rescue of Buffy in the Harvest. Everything in his cultural upbringing tells him that he should be the strong hero to Buffy's damsel in distress, but he knows full well that, in truth, he drools. So, let's not forget to give Xander full credit for being willing to sign on to this project as the weak sidekick to the female hero, and to satisfy himself for looking for little openings where he can be of use. It's not always easy for the guys to swallow their pride like that.