We uploaded 5 shots like this one from beautiful Tamarama Beach in Sydney as a wonderful basis for exploring tides as part of your Maths Session. They can integrate 12 and 24 hour concepts in the Time substrand with height in the Length substrand.
These photographs were taken on 8 and 9 January 2015. Low tide was just 0.4 m at 5:32 pm on 8 January. The next day high tide was at 11:36 am and it was 1.7 m. Can you spot the tide changes when you compare the low and high tide photographs looking to the north or to the south? Tamarama Beach has a bit of a dip down to the sea so the tide is perhaps not as obvious as at other beaches.
If your students live near a beach they can take their own photographs for a mathematical discussion. What cause the tide? Why is it sometimes high and sometimes low? When do the highest tides occur in the year? Why? When are the lowest tides Why? What is the greatest difference between high and low tide in one place in the world?