There are some good ideas in the other answers (for example, working higher on the neck first, to get the chord right, then working your way down). But there are two critical physical reasons why bar chords are hard for beginners, and they don't address these directly:

1. To get good purchase on the neck, the first finger (LH) must use the tiny muscles around its big knuckle (not the big muscles in the forearm that we normally grip with).

2. The other three LH fingers must be independent of the first finger, even though it is working very hard to maintain the bar.

So those two things add up to a big strength and coordination challenge for the left hand. Here are a few things that will help more quickly then simply slogging through difficult changes until your hand hurts:

A) Make sure that your first finger is close to the target fret, is pushing through its middle knuckle (i.e. "arching", so that the middle strings get good pressure), and that your left thumb is offset towards your elbow - this helps the whole left arm put more pressure on the strings.

B) Do this exercise once a day for four weeks to strengthen those tiny muscles around the first finger big knuckle, and I believe that you'll see a dramatic improvement in your barring:

• Stand with your hands hanging relaxed.
• Extend the fingers of both hands all the way out.
• Close the fingers to a fist.
• Easy, eh? Now do it two hundred times, as fast as you can, making sure you snap the fingers open and close all the way each time...

If your hands aren't developed, you'll start to feel it in your forearms, probably, after 20 or 30 repetitions. Work your way up to 200. Since this exercise is "isometric" (no weights) you can't hurt yourself, so go until you are completely slowed down with the extensions, and you have significant "sensation" in your forearms.

This is going to help all of your guitar work, especially the left hand, and if you've been completely extending, you've also been working those small muscles that are essential for barring. In any case, you'll get quicker results than if you just slugged away at chord changes, in my experience.

Finally, for the independent movement of the LH fingers not "tied down" with the bar, bar up higher up on the neck and play scales with the remaining three fingers.

Remember to set yourself a long-term window for improvement - "in four months I should be able to do this" - keeping in mind that playing music is a life-long thing!

There are some good ideas in the other answers (for example, working higher on the neck first, to get the chord right, then working your way down). But there are two critical physical reasons why bar chords are hard for beginners, and they don't address these directly:

1. To get good purchase on the neck, the first finger (LH) must use the tiny muscles around its big knuckle (not the big muscles in the forearm that we normally grip with).

2. The other three LH fingers must be independent of the first finger, even though it is working very hard to maintain the bar.

So those two things add up to a big strength and coordination challenge for the left hand. Here are a few things that will help more quickly then simply slogging through difficult changes until your hand hurts:

A) Make sure that your first finger is close to the target fret, is pushing through its middle knuckle (i.e. "arching", so that the middle strings get good pressure), and that your left thumb is offset towards your elbow - this helps the whole left arm put more pressure on the strings.

B) Do this exercise once a day for four weeks to strengthen those tiny muscles around the first finger big knuckle, and I believe that you'll see a dramatic improvement in your barring:

• Stand with your hands hanging relaxed.
• Extend the fingers of both hands all the way out.
• Close the fingers to a fist.
• Easy, eh? Now do it two hundred times, as fast as you can, making sure you snap the fingers open and close all the way each time...

If your hands aren't developed, you'll start to feel it in your forearms, probably, after 20 or 30 repetitions. Work your way up to 200. Since this exercise is "isometric" (no weights) you can't hurt yourself, so go until you are completely slowed down with the extensions, and you have significant "sensation" in your forearms.

This is going to help all of your guitar work, especially the left hand, and if you've been completely extending, you've also been working those small muscles that are essential for barring. In any case, you'll get quicker results than if you just slugged away at chord changes, in my experience.

Finally, for the independent movement of the LH fingers not "tied down" with the bar, bar up higher up on the neck and play scales with the remaining three fingers.

Remember to set yourself a long-term window for improvement - "in four months I should be able to do this" - keeping in mind that playing music is a life-long thing!