teaching someone to straighten back.

[eltigar]

i have a friend that has started training with me.
hes really skinny, skin and bones and really weak.
empty bar shakes in his hands weak.
im trying to teach him basic stuff, deadlifts sqauts, rows etc.
problem is his back rounds like the sydney harbour bridge, and no matter how ive tried explaining and showing him how i straighten mine, i cant get him to straighten his back.
has his skinniness got anything to do with it?
is he just really unflexable at this time?
any exercises that can help him lower his hips and lift his chest for example?

[dnixon]

How high is he trying deads from? If its just the bar and not the usual height (20kg plates) he may be bending over to reach tje bar too much thus rounding his back. Get him to read ss would be my advice too.

[thebreaker1211]

Maybe less straigtn more arch and keep upper a lil tight /chest up. All depends on what you tell you body do to, may be easier for him to think in those terms