Re: Please check this 'competition entry' for mistakes.
I'm posting my version. The word count is 286 now. See how you like it.
Learning English is not an easy task. It takes time and requires that the learner be very conscientious [requires time and a conscientious learner]. However, we wouldn’t be able to achieve good results without a skillful teacher that leads leading us through this long and arduous process.
My English teacher, Mr Jack, is somewhat unique. His path to this profession was quite unconventional. He was is [just for it to agree with “is somewhat unique”] a self-taught teacher who acquired a high command of English during his many travels abroad. After he returned he came up with an idea: that he could teaching English as a private teacher, as there was a shortage of good teachers in my town at that time [by then]. It didn’t take long before [Before long,] he acquired a reputation as one of the best teachers around. Later he also obtained a formal [I don’t know whether there are “informal” degrees] degree in Teaching English.
I have to confess must say that without the his knowledge and skills of this teacher, I wouldn’t have been able to achieved my current level of English. He can take takes teaching English [at this point, it has already been established that we are speaking of an English teacher, so I believe there is no reason to add up to your word count] to a completely different level. It is not only the knowledge that he has, but also the his methods that he uses and his mere personality which also play important roles. On one side Mr. Jack can be a very funny person. He can be described as ‘cool’, someone with an interesting personality. However, there is also the other side of him: the more serious one. Mr. Jack is well known among students for being very strict and demanding and for being very rigid about his lessons. He definitely appreciates it your working hard and coming up with good results and praises you for it. However, if you are ‘fooling around’ and falling behind with your schoolwork homework, or simply do not meet his expectations (when you should have), you can face harsh and merciless [such adjectives do not sound well for a praising letter; I think it’s better you leave them out] criticism from him. That said, he is a very honest and objective teacher and this approach seems only to serve a purpose: motivate students to work harder and make further progress.
Please be aware that I'm neither a native English speaker nor a teacher.