The End of Primary School

Once upon a time every child had to have his right hand run over his/her head to the left ear before moving to secondary school.
Later, the check was that a child had to be 12years of age before getting into Jss1 in secondary school.
 Soon as long as a child is intelligent, he/she could get into secondary school from primary 5.
Now the age or class no longer matters, as long as the child is intelligent or a parent is just in a hurry and pushes the child to secondary school.
In many schools in Nigeria, primary six (6) has been knocked out, right now, very few pupils are often left to complete primary five, soon primary five will be talked about in past tense.
HOW can we save the educational sector of Nigeria so the primary school is not totally eradicated? What should be the criterion for a child to move into secondary school - is it age, class or intelligence? Are there merits or demerits of completing the '6'  part of the 6-3-3-4 system?

We will be glad to read your feedback, backed up by experience.