First tip:
Never say “The student is incapable to learn”

The parents are very sensitive nowadays for any bad news from their students.
To give bad news, do this smoothly and soft.
Avoid using ” he/she didn’t study” or “He/she can’t understand”
In replace, you can use ” he/ she has some abilities like _ but he/ She needs to use more in the class”

Second tip:
Big good news, bad news, Small good news and advice.

I never started the conversation with bad news. The parents will be in defensive mode if you give the bad news first.
To avoid long discussions and back and forward arguments, start with Big good news or compliments.
Any kind of good info the parents will take this parent’s compliment and this will make space for you to introduce the bad news.
Usually, the parents agree with you on this point but don’t push too much.
When do you feel the stress go higher, introduce the small good news; this will relieve the tension and aggressivity.
And finish with advice.

Third tip

Short advice better than long advice.

Parents don’t have time enough with their kids and because of that long advices are useless.
As a teacher, we also know the students have many topics to improve. However, parents are waiting for a miracle solution and this includes only one dose, as one only big advice.