Secondary teachers have expressed deep concern over the increasingly fashionable idea of schools that take children from nursery right through to Advanced Highers.
Delegates at the Scottish Secondary Teachers' Association (SSTA) annual conference overwhelmingly backed an emergency motion demanding that the Scottish government "exercise caution in encouraging the proliferation of 3-18 schools".
Catherine Nicol, of the union's executive committee, said the case for all-through schools was being made by those who see people only "as numbers on balance sheets".
Members feared that 3-18 campuses, by reducing the overall number of schools, would result in fewer jobs and damage those communities left without a school. Ms Nicol raised concerns around "bullying of young children and exposure to teenage issues too young".
This week, the union also published a survey of 254 members which showed that 65 per cent lack confidence in delivering appropriate course materials for the National 4 and 5 qualifications. Conference delegates argued that, in any case, internal evaluation of National 4 would leave students with qualifications of little value.
"Parents will realise that National 4s are not worth the paper they are written on," said Sally Shearer, of East Dunbartonshire. "We are depriving our poorer children of the opportunity of success because National 4s mean nothing."
She added: "I think the proverbial is going to hit the fan next August, when our children get their results through."
Delegates backed a motion which asserted that an extra year of broad general education would make it "impossible" to achieve more and better qualifications.
The SSTA also called for criminal and civil action to be taken against school-leavers behind last-day pranks, after hearing that lives could be at risk. One boy suffered an anaphylactic shock after an allergic reaction to eggs thrown from a balcony, while students in another school were caught as they prepared to wrap gaffer tape around door handles at an emergency exit.