Writing exercise

This is a writing exercise- a short scene with a stereotypical character (in this case, the stern headmaster) and an effort to make him more "round" as in, not flat, but having dimension, making him more sympathetic.  Tell me if you think I'm getting it.  I'm not sure... I had hard time choosing a stereotype to try and change.  This is the "bullying headmaster with a tender, sentimental side" as suggested by the writing course instructions.  I don't know if I got into the tender, sentiment enough, but I'm trying to keep balance.  Without a full story, just a single scene, I wasn't sure how to condense or include enough information... anyway, comment, tell me what you think.

Headmaster Lucas looked down his nose, through his spectacles and sighed as his eyebrows pinched together.  The student before him cowered.  They always did.  He cleared his throat and the child actually jumped!  Sighing again, Lucas folded his hands before him and leaned down, until his nose nearly bumped against the boy’s. 

“Colin.”  He used his ‘stern’ voice.  It was most effective.

“S-sir?” The boy’s voice trembled, as did his hands.  Please, thought Lucas, just don’t let him wet himself.

“Colin, what you did today.  Sneaking into the kitchens after hours. This is forbidden.”  He raised one eyebrow, squeezing his lips together for a moment, trying to decide what to do with the boy.

“I could expel you.”  The boy’s eyes began to tear up, and his lower lip quivered.

“But, I won’t.  You’re a good student and show promise on the cricket field.  No.  I won’t be expelling you.  Pull yourself together.”  The boy sat up, still shaking, but hope gleaming in his dark eyes.

“Instead, I want you to work for three evenings’ detention periods in the kitchens with Mrs. Gregory. You’ll work off the food you pilfered.  Do you understand?”

“Y-yes, sir.” The boy nodded emphatically. His forehead shone with a light sheen of sweat.  Lucas didn’t smile.  He knew the price of becoming friends with the boys too well.  He would hold on to his power here. At all costs.

“You are dismissed, Colin.”

Colin rose and shakily headed to the large oak door. 

“Oh, and Colin?”  The boy turned just his head to look at Lucas, like a little, frightened owl, eyes wide.

“Yessir?”
“I’ll be wanting you to see Mr. Thomas for discipline tomorrow, as well.”

Mr. Thomas was the one person at Barrington Academy that even frightened Brighton Lucas.  Colin looked about to faint.  Lucas’ stomach clenched, but he held strong. His authority must be absolute.

“Yessir” He whispered, then closed the door behind him.

Lucas sat down again, leaning his head against the high, leather chair back, rubbing his eyes.  He sighed once more, cracked his knuckles and began drafting a memo to Mrs. Gregory.  He knew too well what it felt like to be hungry at night, and he wouldn’t have any of his boys compelled to steal from the kitchens again.  Instead, he would institute evening snacks to be taken before bedtime.  Cheese, bread, and milk, perhaps.  His lips twitched into a small smile.  He might even ask her to let Colin tell the boys about it.  Then he would be looked at as a hero, and might actually make a few friends.  Lucas had been watching him since he arrived three months previous, and his heart ached, watching the skinny lad alone during free hour, wandering beneath the great willows on the South lawn.  It would all come out right, he was sure.