When a language learner consistently makes the same “mistake” it is necessary to delve deeper and find out WHY!
Branded teacher training methods are more often than not very thin on the linguistic ground – actually, very few methods include ANY theory or even understanding on how the brain processes language – and do not equip teachers to identify the source of persistent errors. The result is that teachers cannot address the problem properly and it goes, so to speak, untreated.
Example: *depends of instead of depends on (Spanish & Portuguese L1 students)
When students make this mistake, IT IS NOT A CASUAL ERROR THAT FOSSILISES!
In Portuguese and Spanish, the equivalent expression indeed translates as “depends of”, as the word “de” in those languages usually is translated as “of” in English. Therefore, using the wrong expression is a deliberate tactic of overgeneralisation, using translation and assuming that things are said in the same way as in L1. As such, it has to be dealt with differently!
In such cases, it is often useful to “raise a flag” and create awareness around the issue. It is necessary to point out how the mistake was created in the first place, and to explain the situation, pointing out that generalisation and direct translation sometimes work, but very often do not! And then to practise the correct expression a bit. Just having put a star next to the expression creates a check when the expression is used next and is a start to reversing the process.
This, of course, needs to be done the first time, or as soon as possible after, the “mistake” is first noted. Undoing a :”fossilised mistake” that springs from a deeper level of processing is a nightmare!