Rate/Speed involves a time frame linked to age.
Sequence/Order involves patterns and an order of development linked to body, mobility and intellectual growth - sequence can include an order that's both positive and negative - deterioration.
Rate - what happens at 1 year old, 24 months old, 7 years old ..
Sequence - how things happen in an expected order, sequence ie: breastfed, weaned, full meals. lie, sit, crawl - maybe, stand, walk, run..
Sequence, rate or age at which an individual reaches different stages of development will differ/vary - it could be that one child loses their first tooth at 5 years old and another child when they are 8 - expected development would be that a first tooth comes away at 6/7 - BDHF the sequence of tooth loss is milk/first teeth appear, are lost, adult teeth emerge
the importance is in knowing how each has it's own part to play in identifying the accomplishments of a child, what milestones have been reached and when, they enable charting of a child or young person's development to happen and provide a structure or picture that can measure where a child might be in need of support or extension.
The rate of development is the speed of which a child develops but this can also vary a great deal in each child. For example one child may start walking unaided before their first birthday but another child may not start walking unaided until after their first birthday.
Its important to know the difference between the sequence and rate of development as it helps to meet the children’s individual needs. It helps you recognise if any children have special educational needs and helps you plan to make sure they are getting the help and support they may need.