The former North Lanarkshire Council education convener and ex-leader of Strathclyde Regional Council spoke out over proposals to merge Our Lady's High in Motherwell and Taylor High in New Stevenston at a new £36 million super-school campus on the former Ravenscraig site.
In a letter to feature in the Scottish Catholic Observer, Sir Charles calls for the council to rethink the plan suggesting it should spend "millions" on "reviving" the existing schools.
Parents, the Bishop of Motherwell Bishop Joseph Toal, MP Frank Roy and MSP John Pentland have expressed opposition to the merger plans.
The new super-school would have around 1,400 students and take pupils from Bothwellpark ASN High which caters for those with extra support needs.
Sir Charles wrote: "Concerns raised that the proposal is more about profitably selling the school sites to house building firms than for educational purposes are understandable as under Travel to School rules, students must reside over two miles away before being eligible for free travel and it is doubtful if many of the 2,150 youngsters could apply, while road traffic in that particular area is about the worse in the county.
"I believe a couple of millions could be spent on reviving the two schools, which move would be economically and educationally sensible as well as being acceptable to the dioceses and the two communities."
North Lanarkshire Council's learning and leisure convener Cllr Jim Logue said: "The projected roll of the new campus is not 2,150 as Sir Charles suggests, but 1,500. Sir Charles must remember he merged four schools, two non-denominational and two Catholic, into two, with rolls of 1,100 and 1,400, in Coatbridge.
"Merging schools and creating larger campuses addresses the very real and costly issue of under-occupancy, leads to vastly better facilities and improves the educational opportunities of our young people."