All weather science starts with observing the weather. At the simplest level, this requires no instruments other than the naked (or partially clothed) eye. Cloud type and cover can be assessed in this way. Other readings require proper instrumentation.
Instrument readings are taken throughout the UK by a team of trained observers at 0900 UTC each day.
Organised system of readings was introduced following the invention of the telegraph, which allowed weather data to be passed quickly to the people who needed to make use of it immediately.
When people talk about the hottest summer "since records began", what they mean essentially is since 1848, as it was since this time that there was an organised collection of weather data on a daily basis. However, climate researchers will gather data from a huge range of sources to try to build up a picture for what the weather was like on specific days hundreds of years ago.
The data collected at a typical weather station are:
Maximum and minimum temperature
Rainfall amount and time (tipping bucket gauge)
Air temperature, concrete temperature, grass minimum and soil temperature
Dew point temperature
Wet and dry bulb temperature
Wind direction and speed
Gust speed and direction (and time)
Relative humidity
Sunshine duration
Visibility
Cloud cover
Barometric pressure and tendency
Present weather (and remarks on particular observed phenomena)
Students need to know about how weather is collected and the instruments that are used in a typical weather station.
Would be good to have a visit to an actual weather station.
The XCWEATHER site has some good wind details
These would allow students to follow the change in atmospheric circulation and air masses.