Thecrabbypatty, I take it from your comment on googling that you have your own concept of what it means, and that you tend to favour that over any sort of detailed or authoritative analysis.
So at the risk of boring you to death, here goes...
There are all sorts of legal ramifications to being 'in loco parentis'. The role confers certain rights and there are also responsibilities, among them protection from harm. There is in addition the duty to safeguard the human rights of students.
The ins and outs of 'in loco parentis' - how teachers are expected to conduct themselves in relation to students - are governed by law, unlike all the myriad interactions between children and parents, where other parameters are in operation. Above all, a teacher is expected to do what a 'reasonable parent' would do, not a parent who thinks it's ok to go apeshit.
The role is custodial and tutelary. It allows for reasonable and appropriate force/physical contact to be used in order to protect a student or students or staff from harm. It does not encompass losing your shit, or even pretending to, because of the duty to protect from harm.
While acting 'in loco parentis' teachers and school authorities also act as surrogates for the state in many respects. Teachers are not fully engaged in the parent role therefore. There is acknowledgement that the pastoral responsibility in the area of safeguarding, for instance, is to the students, not their parents, and teachers are not acting in the interest of the parents when acting in a safeguarding role. Teachers in addition may search a student's belongings and even a student's person for forbidden or illegal items such as drugs or weapons. The role as surrogate for the state illustrates that teachers are held to a higher standard than parents and expected to exercise a judgement that is not only professional but open to scrutiny. Above all, the aim of preventing harm is underlined in these roles.
It's not just a matter of nose wiping, hand holding, and being an adult helper, and it's certainly not a matter of doing what you assume a parent would do, given sufficient provocation.
I have seen parents verbally abusing children, and I have seen the effects on those children. You seem to assume all parents lose their shit, and you seem to assume all parents would be happy to let you do. I do not think that assumption would stand up to the requirement to act as the 'reasonable parent' and the overarching interest of teachers in preventing harm. If you want to keep on arguing that loud public humiliation is ok for a parent to do and therefore it is fine for you, it's your dime, as they say.
But be aware that as a teaching professional, you are not covering yourself in glory by doing so.
www.teachers.org.uk/files/the-law-and-you--8251-.pdf
The NUT digest of what in loco parentis means in the context of school trips:
"In practice, this means that teachers must provide supervision of the pupils throughout school journeys or visits according to professional standards and common sense. Reasonable steps must betaken to avoid exposing pupils to dangers which are foreseeable and beyond those with which the particular pupils can reasonably be expected to cope. This does not imply constant 24-hour direct supervision. The need for direct supervision has to be judged by reference to the risks involved in the activity being undertaken. It may not always be sufficient to give instructions to pupils. The possibility that there may be challenging behaviour has to be taken into account, together with the risk the pupils may encounter if they disobey instructions. Equally, teachers may take account of the ages and levels of personal responsibility of their pupils...
...Teachers should not participate in journeys or visits which they believe are not being adequately prepared and organised. Any concerns should be raised with the head teacher.
Where journeys are organised within schools, responsibility for establishing that proper preparation has been made and that proper supervision will be provided is ultimately with the head teacher. Head teachers may delegate this function to the educational visits coordinator (EVC). Head teachers should prohibit journeys and visits if they are not satisfied with the arrangements made..."
www.teachers.org.uk/files/the-law-and-you--8251-.pdf
It seems to me that a trip to Alton Towers is a ridiculous thing for any school to contemplate, given this NUT advice, and so it is reasonable to question the professional judgement of the teachers who planned and participated in it. It has all the ingredients of a disaster.