This is good advice. I would like to add a few things:
1. Spend time addressing what happens/where/and when - what part of the tongue? where is it touching? what direction does it move? GREAT, now all of those things need to happen at the same time.

2. Asking THEM about what they hear will go a long way. So as you go down the line, ask the previous person "did he sound like you?" If not, then ask "why not? too long or too short?" Getting them involved and engaged in the process is the beginning of teaching them how to hear errors and correct them.
Once you get there, you can also ask "what can she (physically) do to play the note the same way you did?"

Also, with younger groups I sometimes have luck assigning a number. For example 1 is our shortest articulation, 3 is normal, 5 is the longest with most weight. Then I can always ask "what number articulation is this? what number did you actually play?"

Above all, be persistent, and know that it is not an immediate fix. Don't be afraid to address articulations while learning new music instead of later on.