Exasperated by the lack of discipline

[Bassim]

Are my sentences grammatically correct?

Exasperated by the lack of discipline in his teenage sons, Peter hired a former soldier to instil discipline in them during a summer holiday. After two months, the naughty boys had undergone a transformation into well-behaved teenagers, who never answered back and respected everyone. Peter asked the soldier what was the secret of his success, and the man laughed and told him that if there would ever be any kinds of problems again, he could call him any time.

 

[Charlie Bernstein]

Are my sentences grammatically correct?

Exasperated by the lack of discipline in his teenage sons, Peter hired a former soldier to instill discipline in them during a summer holiday. After two months, the unruly boys had undergone a transformation into well-behaved teenagers (no comma) who never answered back and respected everyone. Peter asked the soldier what the secret of his success was, and the man laughed and told him that if there were ever any kinds of problems again, he could call him any time.

That's not a situation where we'd use "naughty." Its connotations are too childish or infantile. Maybe others here can suggest some other words that would fit better.

 

[Bassim]

Charilie Bernstein.

"Instil" with only one "l" is BrE.

 

[teechar]

I would prefer "had been transformed into" to "had undergone a transformation into".

 

[Tdol]

Charlie Bernstein.

"Instil" with only one "l" is BrE.

I am sure Charllie will instil that in his memory for future reference. BrE users are normally the double -l-ers, but not here.