I have a friend I just introduced to shooting and he is left handed.  Holsters, mag pouches left handed is easy.

What does he need to do or buy for mag changes and dropping the slide stop.  How does that work and will wilding extended controls be required?

Hell no. He doesn't need anything, just practice. Slide lock with his index finger and either index or middle for the mag release.

"What does he need to do or buy for mag changes and dropping the slide stop." You grab the slide, pull back and release.

The only mod on the glocks that I have would be to dremel the bottom corner of the mag release button. Personally, I do not believe in extended controls.

Quoted: Hell no. He doesn't need anything, just practice. Slide lock with his index finger and either index or middle for the mag release.

Yep.  

And tell him not to get an extended mag release.  I put one in and being left handed it was exposed (more than the stock) and constantly popping the mag out.  I kept finding my mag not seated and glad I never had to fire it in an emergency.  It wouldn't be good to fire one round and have the mag drop out.  

It's better for leftys 'cuz we can hit mag release w/ trigger finger or middle finger while you fruity righties have to use you thumb.  Watch how much a right handed person has to switch their grip to release the mag.  Also use sling shot method.  It's the only way I do it w/ any handgun.

Quoted: Quoted: Hell no. He doesn't need anything, just practice. Slide lock with his index finger and either index or middle for the mag release. Yep.   And tell him not to get an extended mag release.  I put one in and being left handed it was exposed (more than the stock) and constantly popping the mag out.  I kept finding my mag not seated and glad I never had to fire it in an emergency.  It wouldn't be good to fire one round and have the mag drop out.

+1000  Took the extended mag releases off both my 34's and 35's after I would drop at least one mag every 200 rounds or so.

Quoted: It's better for leftys 'cuz we can hit mag release w/ trigger finger or middle finger while you fruity righties have to use you thumb.  Watch how much a right handed person has to switch their grip to release the mag.  Also use sling shot method.  It's the only way I do it w/ any handgun.

HUGE +1

Being a lefty with Glocks is great.  I actually prefer releasing the mag with my trigger finger.  I train right-handed as well, and I have to adjust my grip a lot more to release a mag with my thumb.

I too am a lefty.  Average build and my gun of choice is the G21.  I think that if I were a righty I would not be able to release the mag with my thumb as the grip is so large.  I really feel that being a lefty is very big advantage, especially with this particular gun.  The index finger release was also the way I worked my 1911 before I became a convert to the "evil plastic pistol".  I am sure that my next statement will cause arms to flail but I shoot a good bit of IDPA and 3 gun and have never hit the slide stop.  I guess with arenaline I ram the mag home so hard it causes the slide to go forward by an artifical stop relaease.  I kid gloved the gun first few range session (scared of breaking plastic, WHAT AN IDIOT I WAS).  When I started runnning wide open I noticed that hitting the slide stop was never needed.  As a down side I have noticed the dings on the mags from this over insertion that causes the release.  Other than that, through over 3700 rouonds nothing else has broke from my caveman approach to mag changes.  As stated in another reply pull the slide back if needed and don't piss with releasing slide stop (also how I ran my 1911).