Academic journal article Australian Primary Mathematics Classroom

When near Enough Is Good Enough: 8 Principles for Enhancing the Value of Measurement Estimation Experiences for Students: Tracey Muir Outlines Eight Guiding Principles for Helping Children Understand the Importance of Estimation When Measuring at Work, in School and in Our Everyday Lives

Academic journal article Australian Primary Mathematics Classroom

When near Enough Is Good Enough: 8 Principles for Enhancing the Value of Measurement Estimation Experiences for Students: Tracey Muir Outlines Eight Guiding Principles for Helping Children Understand the Importance of Estimation When Measuring at Work, in School and in Our Everyday Lives

Article excerpt

Everyday, adults and children encounter situations where they have to make judgements about "how much" or "how long" or "how many". The significance of estimation as an ordinary, everyday and natural aspect of measurement needs to be conveyed to students through their mathematical experiences (Department of Education and the Arts, Tasmania, 1994). Many students, however, tend to view estimation as a difficult technique where success is dependent upon how close the student's estimate is to the teacher's estimate rather than a useful and practical experience. Teachers and students need to realise, however, that estimation is not simply guessing, but rather an informed judgement. Research has shown that estimation employs mental computation, rewards flexible thinking and helps dispel the "one-right-answer" syndrome often associated with exact computation (McIntosh, Reys, Reys & Hope, 1997). Based upon my reading of recent research and experience as a classroom teacher, I have devised the following eight principles of estimation which may assist teachers with making estimation a more purposeful and enjoyable experience for students.

1. Estimation is useful

Fundamentally, measurement is about "making comparisons of one thing with another according to a selected attribute" (Department of Education and the

Arts, Tasmania, 1994). Estimation is an integral part of everyday life as many measurement situations do not require exact measurements (Hodgson, Simonsen, Luebeck & Anderson, 2003). I recently asked a class of Grade 4/5 students to "brainstorm" a list of the times where they had used estimation, rather than a more "exact" measurement as a result of using a formal measuring instrument (1). After initially focusing on school-based mathematics lessons, such as estimating how long the tennis court was, they eventually generated a list which included experiences such as judging how much cordial to place in their drink bottle before adding water, whether or not they had enough money to buy something at the canteen, which queue to join at the canteen counter and how much paint to place in the paint palette. This highlighted how much estimation was a part of their everyday life and that often approximations or estimates are "near enough". Out of the discussion arose an observation that estimates are used frequently in cooking and that "my mother never measures anything--she just adds what she thinks". This was an opportunity to discuss when exact measurements are necessary (see Principle 7) and also provided a springboard into discussing which occupations use estimations.

2. Estimation should be related to real life

Many professionals rely on making appropriate estimates in order to carry out their work successfully (Adams & Horrell, 2003). Adams & Horrell (2003) interviewed a number of professionals about how and why they use estimation in their work and their findings provide a good starting point for generating student discussion in this area. Students were able to identify, for example, that umpires and referees use estimates of time and length in many sports, a chef uses taste and touch to develop estimates for a "pinch of salt" and the assistant at the delicatessen has developed the ability to estimate the approximate amount of ham asked for by the customer and then adjusts accordingly. It was agreed that it would be rather frustrating for the customer to have to wait while the ham was painstakingly measured out; the assistant also has the ability to estimate according to whether it is a request for a "kilogram" or $4.00 worth of ham.

While estimation saves time for many professionals, for others, such as police officers, it helps to validate measuring tools and methods (Adams & Horrell, 2003). Professionals also estimate when more exact measures are not required. For example, customers who employ builders or landscape gardeners will often request a quote on how much the task will cost and how long it will take, rather than how many bricks will be needed and how much cement needs to be mixed. …

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