Is it typical to have trouble getting out the high D note? Because when I play it with other notes, it comes out fine, but when I have to play high D continuously, it jumps down to the middle octave after a few times.

I use the middle D fingering, but half-holed. This is probably the problem, but I am not too experienced.
I also don't think I have a high D key because the school bassoon I use is a cheap model.
I also am aware of the difference between reeds and also their opening sizes, but the reed I use now should be fine for all the notes I play.

I appreciate any advice from experience bassoonists/musicians!

High D is a tricky note - even after 30 years of playing I cannot get it reliably but then it appears so rarely in the music I play that I've never bothered too much.

Even if you have a high D key (An extra one for LH thumb above the high C) there is no guarantee it will happen easily. There are many reasons for this including:
Bassoon & bocal not up to it.
Reed not suitable
Player not up to it - not enough breath support & incorrect embouchure.

There are numerous fingerings for this note (8 in one book I have - none of tehm being anything like the one you're trying!) & you have to try until you find one that suits you & your set up. The 'standard' one in most charts is LH 00X + low eb & high D or C; RH 00X + Ab

Good luck.

Exactly which D are you talking about? The one just above middle C or the one an octave above that? If you are in high school, I'm amazed you would have much use for the second one. Does the music you are playing actually have you playing that note? Or are you just trying to do it for the fun of it?

I think you're right Drew - I was making things too difficult.

Thank you for your responses. I was able to ask a professional bassoonist as well, and the text below was his response (which also answers Drew's question about which D note I use). For my problem of playing the note in rapid succession, his solution of holding the flick key the whole time was helpful.

"The High D you are talking about is not the same D in the response. You are talking about the 3rd octave D above the staff... there is another D above that is called high D. You are talking about overblown D.

There are 3 solutions:
(1) My suggestion is make sure that you vent (sustain flick) during the duration of the time you play that D.

(2) You can also add the Bb key in the right thumb (that usually fixes it) or as a last resort...

(3) You can use the long fingering for that D (add fingers 2 3 and 4 in the right hand)"