Oh, I'm in a really big trouble. You cannot even imagine how difficult it is to define the number one mistake of all times.
#1 Adding -(e)s
Wow! I think students mix everything in so many ways with these endings. The most popular grammar topics you need to practice for avoiding this mistake:
- sometimes students do not know the rules for adding ending -(e)s;
- someone forgets to add -(e)s after the verb in 3rd person singular;
- students usually missuse do and does;
- the same goes with don't and doesn't;
#2 Sentence structure with auxilary verb 'to be'
This one is one of my favourite too.
Usually when students learn do (does) they forget about 'to be' at all. Normally, a teacher can hear something like this in the classroom:
- I am do this exercise every day.
- He is not play piano.
#3 Word order mixed up
Most talented students are able to mix up every possible variation of word order.
The main trick here for the teacher is to make students understand the core structure SVO.