Yes always. All children should have the opportunity to stimulate their intelligence and develop all their abilities. Even if you think that your child is not very intelligent or that there are other children smarter than him ... you should never minimize his potential. Your child may not stand out in some things but quite possibly he can stand out in others.
The first thing you have to do to be able to enhance the intelligence of your children is not to compare them with others. They have their own idiosyncrasies and you don't have to compare it to anyone but themselves. You can compare their latest results with the previous ones, but if they have to compete with someone, always be with themselves.
If your son gets low marks in school, don't think that he doesn't have the capacity for more ... think about how you can help him to improve his ability and see that he is capable of achieving whatever he sets his mind to. Either seeking psycho-pedagogical help, private lessons or motivating him so that learning (of anything) feels like something fun that will bring him many things.
Your child may show you that they want more challenges, that what they are learning is not enough, and they want more. Look at what facets your children stand out to enhance it. Maybe it's in language, in art, in sport ... And when you enhance this facet, you will be surprised at what it can achieve. All children have the right to excel in something, in addition, they also have the ability to do so.
Encourage him with good words, telling him that if he makes a mistake, it won't happen. Because one way to enhance the intelligence of children is to teach them that mistakes are our great teachers and that thanks to them we can achieve great things ... A mistake is an opportunity to try again what went wrong the first time.