International Student With a UK Visa Question

This answer came rather late but I'm curious which visa did the enquirer traveled on?

Educational visits to schools in the UK are permitted activities for visitors on Standard Visitor Visa, as long as it is not the main purpose of the visit to the UK. The official link is here: https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules

Study

25 Visitors may carry out the following study:
    (a) educational exchanges or visits with a state funded school or academy or independent school; or
    (b) a maximum of 30 days study on:
        (i) recreational courses (not English language training);
        (ii) a shourt-course (which includes English language training) at an accredited institution;

provided that the main purpose of the visit is not to study and the study is not at a state funded school or academy.

Since observation does not count as a course but more of an educational visit to broaden horizon and deepen educational understandings, it should be taken as activity (a) in above picture.

Standard Visitor visa

https://www.gov.uk/standard-visitor-visa/overview

If you visit the UK on business

You can apply for a Standard Visitor visa if you want to visit the UK for business-related activities, eg:

you’re coming to the UK for a conference, meeting or training you’re an academic and are doing research or accompanying students on a study abroad programme.

See Gayot Fow's first comment to your question.

You are pursuing a Postgraduate Certificate in Education (PCGE). This is a "one-year higher education course in England, Wales and Northern Ireland which provides training in order to allow graduates to become teachers within maintained schools". Before starting the course the student is required to spend two weeks of 'observation' in a primary school.

Your question is what type of visa is required to perform the required observation. I wanted to answer this question in a canonical way first so it can provide a reference point for all related questions having to do with international students. And after that I can take up your specific question.

Canonical Answer

What follows may seem a bit baroque for the community here on Travel, but there is a lot of grey areas and ambiguity about what can happen on a visitor visa (which is our domain) versus other visa types (which is the domain of our sister site at Expats). Much of the ambiguity in the rules is intentional for reasons that are out of scope here.

Background. All educational institutions in the UK who are offering in-country programmes to international students are required to have a Tier 4 sponsorship license. This license enables the institution to provide the prospective student with a certificate that can be used to apply for a visa. Technically, the certificate is called Confirmation of Acceptance for Studies and students using internet forums refer to it as their "CAS".

Your education provider will send you a reference number called a confirmation of acceptance for studies (CAS) once they’ve offered you a place on a course. You’ll need to enter this on your visa application.

Source: Tier 4 (General)

In order to qualify for the license, the institution must have an infrastructure in place and part of the infrastructure is to have an "Authorising Officer". Reporting in to the Authorising Officer are several other roles that must be in place before the institution can obtain their sponsorship license.

When you apply for your licence you’ll need to allocate these 4 roles to members of your staff:

Source: Apply for a Tier 4 Sponsor License

TL;DR

With this knowledge we can be confident that any international student with a visa question at any UK institution can present their question to the "Authorising Officer" (or one of his required staff) for resolution.

Individuals who rely solely on internet forums are asking for trouble because the student rules are subject to change (up to twice a year); forum archives and personal experiences on the other hand are static to a particular point in time and hence frequently out-of-date (this site is no exception by the way).

Specific Answer

I do not agree that the Standard Visitor Visa is appropriate for your "observation phase" because it does not have the structure and organisational rigour of meetings (conferences, trade shows and the like) that a visitor can undertake. Instead, I think the activity is part of your curriculum as a PGCE student, and so the appropriate visa is the Tier 4 you obtained (or will obtain) to take the course.

In order to confirm my assumptions, I followed the above "canonical answer" and called the "Authorising Officer" at the University of Brighton. He was out for the day and so I spoke with one of his required staff, the "International Liaison Officer" (one Mr. Jamie Henley). We discussed your question and he confirmed that the PGCE observation phase is covered by a Tier 4 Visa and not a Standard Visitor Visa.

That constitutes your answer. Since the required visa is a Tier 4, all future questions should be taken up on the Expats site (or with your Authorising Officer in the first instance).

Notes:

• information on UK Visas and Immigration's (UKVI) required organisational structure are at Apply for a Tier 4 Sponsor License;
• Mr Henley gave his permission to cite his name in this answer;
• Trying to get an answer to a specific question out of UKVI is not generally productive for lots of reasons that are out-of-scope here;
• in many cases the Authorising Officer is a grand old and respected academic whose presence is to dignify the institution's relationship with UKVI. They may not even have a solid working knowledge of the rules. Accordingly questions from students are handled by a lower ranking staff member (who absolutely must have an excellent knowledge of the rules);