Yeah I think they can, if they get strong enough, control the Avatar state. Because whenever they showec an Avatar and the Avatar did something amazing their eyes glowed and they they unleashed a powerful attack. Who knows maybe the Guru is supposed to teach Aang how to control it.

Wrong place for this, this is more show based than bending because you have no leads to any bending art, just a general thing.

yes im sorry i could have sworn i clicked on bending arts im gonna move it!

aang is only twelve. he is strong, but the other avatars were incredibly strong. plus, aang is techniquely controlling more than any other avatar had to. he has to control everything roku had to, plus himself. and he hasnt mastered the four elements but he seems to obtain the ability to use them in the avatar state. you are probably right about the sudden light being the avatar state being controlled.

Not much is known about the avatar state. All we know so far is

1) it contains the powers of all the avatars
2) triggered only under the most stressful of times
3) the avatar line will be lost if an avatar is killed in the state
4) allows unbelievable powers, but exhaustion afterwards.

You can't really make a theory on something this simple. But for the sake of attempting my theory is as follows

The Avatar state is only fully mastered and controlled when the avatar has completed his training and contains the wisdom of the years to come. Aang is young and hasn't seen what raw power can truly do, at least being attacked by it. (exclude the dream since he didn't fully feel the pain)

Aang likely won't control the state until well into the 3rd of 4th book, and even then it still won't activate until the stress is unbearable.

thats my thoughts. Heres a nickel

For point of reference (and by the way this post is a SPOILER FOR 'THE EARTH KING' AND 'THE GURU' so stop paying attention if you haven't seen it yet)...

...the Guru at the Eastern Air Temple sent a message to Aang stating that he would help Aang learn to control the Avatar State.

End Spoiler.

To move on from this point... are you all addressing 'controlling' the Avatar State as using its powers without the glowing-eyes-pure-instincts thing? or are you addressing 'controlling' the Avatar State as allowing the glowing-eyes trick to be done with conscious control INSTEAD of with pure instincts?

Well, in the first episode of the second book, Rokku teaches Aang about the Avatar State. He says it's a defense mechanism. During this clips of past Avatars rush past. In each, the avatar's eyes flash and he/she commits an incredible act. I believe controlling the Avatar state means being able to enter it willingly rather then by defense like the past avatars did.

Kalken does have a point, there. But, I guess you could maybe eventually learn to control the Avatar State. Truly, I don't really know, but maybe you can..... *ponders* If Aang could control the Avatar State, then what would be the point of learning all of the elements? He could just *poof* Avatar State himself.