As a teacher, you need to remember that the problem the students are facing with chords could be a mental processing issue and likely not a coordination issue.
The problem is almost always with their brains and not really their hands.
Keep this in mind so as to ensure you allow their process towards prowess to be much faster.
First, get the students accustomed to keeping their strumming hands working in time no matter where they are with fretting. There should be no time wasted waiting for the fretting hand to get its sh*t in order. Tell them they must keep strumming. It will allow them to keep the rhythm. And it will make them progress much faster.
You can also get them to grip the strings hard then relax and repeat- while playing the chord. This will train the brain to work the fingers in unison and not one at a time. Get the student to repeat this until they can do it well.
You could also try a rapid fire chord change with the fretting hand only and quickly! This is another way to train the hand and the brain to work on time.
Another tip is get them to try and play the A chord with just one finger, and it doesn’t have to be same finger. They can use their middle finger, index finger or ring finger. But the idea is that it will aid the fret hand speed.
Another interesting tip you can give them is to keep their mind on the NEXT chord and not on the one they are already one. That can help make transitions much faster.
As you will notice, most of these tips are of a physical nature but if done over time, they affect the brain and how it makes the students play. A lot of practice will get their brains accustomed to the new skills and it is likely that all their chord problems and chord transition challenges will slowly vanish.