UK Student Visa Guide & Assessment:

You can apply for the student visitor visa for UK if; you are undertaking a short duration research project, attending a part of your overseas course in the UK, and learning English as a foreign language. You need to; be of legal age that is about 18 years, have a valid offer to take a course at an accredited university, be financially capable to undertake such a course and able to pay for your exit trip. You will need to provide credible proof of all of these eligibility criteria.
The university or institute in which you can undertake a course needs to be licensed to sponsor Tier 4 migrants. Other than that, any institute recognized by Accreditation UK, Accreditation body for language services. British Accreditation council or Accreditation service for International colleges, can render you eligible to apply for a student visitor visa. 8 other signified Licensing bodies in the UK have listed institutes, studying there can also let you apply for a student visa.

While on a student visitor visa you cannot; enroll in a state school, start a business, enter a marital contract, request visa extension, bring dependents, and receive public funds. The duration of stay is limited to 6 months for short course, while 11 months, with an extension of English language course. The standard visa costs £83 while the extended visa costs £150.
Tier 4 General Student Visa can be applied for by persons above the ages of 16 years, have fluency in written and oral English, are financially stable and do not belong to Switzerland and EEA. The maximum duration of your stay is mostly dependent on the course you are undertaking, usually 6 or more months. The visa fee is £310.
If, you are less than 18 years and more than 4 years of age, then the Tier 4 Child Student visa can be applied for. To qualify for the visa you need to, be permitted by your guardian or parent, be financially stable, not in Switzerland or EEA countries, and already accepted in a course. Being 16 or less you can apply for a course which might be 6 years long, and can have a 4 month extension. If, however, you are 16 years to 17 years of age, the maximum course length you can apply for is 3 years with an extension of 4 months. The visa fee is £31.