Introducing negative numbers

What does research suggest about effective ways to introduce negative numbers?

The idea of negative numbers may feel odd and counterintuitive to students
Students need to have a perception of number as both counting and measurement, as preparation for learning about negative numbers
An early focus on subtraction and multiple concepts of zero is important
Acknowledging negative numbers when teaching subtraction may be effective, but waiting until students have a sense of the structure of number systems to explore them more fully is suggested
Students may be confused between negative numbers, decimals and fractions
Teachers should carefully consider their language around negative numbers, especially the use of the words ‘minus’ and ‘negative’
There are many useful models and metaphors for teaching negative numbers, but no one is totally representative on its own and all have limitations
Students should understand the minus sign in at least three senses: unary, binary and symmetric