Bulge classes can be a negative, in dcs school the LEA has doubled 30 to 60 for a few years, now LEA pulling the plug as have realised not practical due to the site to make into double entry form. Nothing to do with nimbyism, just when they actually bothered to visit the site they realised it couldn't be done. Now many of those who benefited from the bulge years are facing a year or more of sleepless nights to see if all siblings get in, as numbers are close to the wire, and they live the furthest out. The next few years, even those living next to the school might not get places, but will be in a black hole for any other school. The people who have a long term, worry free gain are those with only children, or who live a long way out but happened to squeeze both children into the bulge years.
The people who got in on the bulge years live further away and so are more likely to drive. The lunch hall is a military operation, and woe betide any reception child who takes more than 20 min to eat lunch, or the ks2 child who is hungry before 1. The numbers of children needing places is even higher over next few years, so due to lack of planning there will now be even fewer places available for first borns. Ds's class will be almost all younger siblings, so will probably be more streetwise than a mixed class, and will know each other more due to being in playground, going to nursery etc, so will be harder for first borns etc to break into.
Taking either 45 or bulge classes alternate years (as many people have a 2yr age gap) would have reduced these problems and led to more sustained growth (though not sure I entirely like mixed classes). I don't have a problem with the principle of expansion, if the school is able to take it and sustain it, but these assessments need to be done in advance so the best solution can be found for each school/area, rather than as a knee jerk reaction when mrs mumsnet can't get her child a school place in a 15 mile radius. As many have said the LEAs haven't prepared for the numbers involved, which must have been apparent when we all started trying to book in with our midwives only to realise that she was fully booked for next 3 weeks.
Lets be clear I don't want children travelling miles to a struggling school, which will lose students as 'better' offers come up over the years, I don't object in principle to expansion (I could have gone on about the lack of playground space, assembly space, wrap around care spaces, afterschool club spaces, nursery places etc), but it needs to be managed and planned otherwise it is just creating a bigger timebomb. I am lucky as we were there before the expansion, so confident for ds's place, and I don't have a first born due to start soon. Controlled expansion and new schools, yes, random dropping of portacabins (which are actually nicer than some existing classrooms), and lack of foresight/planning to see if the provision can cope with the expected intake for next 4+ years, doesn't help in the long term.