I think the spawn block is the 'neatest' solution, however if you really want to go down the command block path you could use the following.
1 - /tp @a[score_deathcount_min=1,score_deathcount=1] x y z (these coords should be on top of another pressure plate)
then you would need to set up a 'dummy' scoreboard with a name like 'wait'
when you teleport students you want to also give them a wait score of 300
2 - /scoreboard objectives set @a[r=2] wait 300 <- this is under the pressure plate you teleport students to,
then reset their death count
3 - /scoreboard objectives set @a[r=2] deathcount 0
you will then need to teleport them away again, to your wait room,
4 - /to @a[score_wait_min=300,score_wait=300] x y z (these coords should be to your wait room.
Underneath the wait room you will need another command block that is
5 - /scoreboard objectives remove @a[r=y,scoreboard_wait_min=0] wait x (where x is a number that is being subtracted and y is the radius of your wait room, you will want to adjust this depending on the speed of your clock).
Now that we have all the commands out of the way here is how I would set this up.
Wait room is at world spawn, underneath world spawn is a redstone clock running command blocks 1 and 5
Intermediate teleport room can be anywhere, just not really close to the wait room and the blocks need to be 'triggered' in order, 2 then 3 then 4
Clear as mud right?
The reason we use world spawn for the clock is because those chunks are always loaded, I would recommend a hopper clock too, less lag is caused by these and there are plenty of tutorials on how to create them.
Elfie.