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The Australian Bureau of Statistics has a collection of educational resources for primary and secondary maths - "Bringing Data to Life in the Classroom". Some good activities are the "Population Clock", "Country of Birth", "Participation in Sport" and "Misleading Graphs".
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ConCensus is a site where you and your students can investigate a huge range of data sets from the Australian Bureau of Statistics. It has been developed by ABC Splash as an education resource to allow the visualization of data collected from the 2011 Australian Census, including languages spoken at home, gender and age demographics, occupations and how people travel to work. You can also create your own surveys using the MyCensus tool and visualize the data collected in a few different ways - coloured blocks or circles, a donut-shaped pie chart or a table of figures.

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Authentic Assessment Toolbox has examples of assessment activities for Number, Space and Chance (Probability). Some really nice authentic tasks here, contributed by teachers. "Make the Game Fair" and "M&M random sample" are popular with students.
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Cut The Knot , by Alex Bogomolny, is about taking maths games seriously - using Java applets (1997 to 2004). There are some classic maths puzzles here, including "Frogs and Toads", "The Three Jugs" and many more.
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Hot Chalk Math Matters is a series of videos with supporting problems. "This 30-segment video resource focuses on ninth grade Pre-Algebra and Algebra. What makes this unit different from most? It revolves around the world of off-road motorcycle racing. Team HotChalk worked with a group of young HotChalk-sponsored cyclists, videotaping them jumping off ramps along dirt bike tracks and racing up the golden summer hills of a ranch overlooking the ocean in Central California. Courtesy of math teachers Jason Dyer (Pueblo High School, Tuscon, AZ), who scripted out the 'real world' algebra problems, and John Villavicencio (Berkeley High School, Berkeley, CA), who explains the step-by-step solutions in each segment, we are bringing you our first homemade model of YouTube-style learning, "Off-Road Algebra."
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HOTmaths is not free, but has a few sample lessons, which are quite good ("Symmetry", "Keeping the balance" and "Distance/Time Graphs")
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Museum Victoria has a Mathamazing school-based education kit (pdf) with some unusual activities, such as Bakuba networks, tessellations and a mobius strip.
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National Library of Virtual Manipulatives is an excellent library of maths interactives, searchable and categorised by age and topic.
Some of my favourite applets on this site include Algebra Balance Scale (one with just positive numbers and another with negatives); Prime Factor Trees and drawing a line using a point and the gradient.
This site uses Flash and Java, so isn't accessible using iPads. If you have difficulty accessing the applets you may need to change your browser (use Chrome instead of Windows Explorer for example) or update your Java software.
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The NRICH Primary Maths Clubis a super spot to visit - loads of ideas - Join their Maths Online Club. "The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice." Lots of problem-solving and critical thinking required at this site. They have new problems uploaded on the first day of each month.
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National Centre for Excellence in Teaching Mathematics from UK, has professional development resources for teachers.
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Open Ended Maths Problems from the Franklin Institute.
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That Quiz is a site with customisable problems in integers, fractions, geometry and other maths concepts (as well as science!). Students get feedback about the questions they got incorrect.
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ThinkMaths is a UK site with a downloads page where you can access some great activities for students, including "A mile of pi", a hexaflexagons worksheet, instructions for building 3D fractals and more.
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Tessellations is an outstanding site for viewing and creating wonderful tessellated artworks. Examples from Escher, Seth and Dr David, as well as student-created works on display.
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Printables of nets for 3D models of 16 shapes from SEN (Special Education Network) Teacher. Print out onto thin colored card and students can construct them using tape.
Ambleside Primary Maths Games - Numeracy Hour at Ambleside Primary
Ask Dr. Maths - Part of the amazing online maths forum. Get your questions answered here!
Beat the calculator - Tips for Maths - Excellent!
Cartesian Cartoons - a site where you can find lots of cartesian co-ordinate cartoons and student work
Cyberchase - interactive games based on the ABC TV cartoon.
Dianne Siemon resources for the Department of Education in Victoria.
Egyptian Maths - Excellent for exploring number values
Everything about the Abacus - Excellent site!
GirlTech - excellent experiments and Maths activities.
Math-Aids - where you can dynamically create your own worksheets
Maths games from Learning Today blog
Mathsnet - ideas and interactive pages
Maths Zone - Instant Maths games KS 1/2 is for up to Year 5 and KS 3/4 is from Year 6 to 10 in Australia.
Mayan Maths - Explore ideas about the Mayan number system here.
Numeracy Resources - Made by a school in Yorkshire - Great resource for maths games. Try the brilliant SNAP games.
Primary Resources - lesson plans and worksheets. Follow the links.
Resource Library from the Victorian Department of Education, including assessment tasks and rubrics.
Task Type and Mathematics is a set of classroom activities that were designed by Victorian teachers as part of an Australian Research Council (ARC) Linkage project scheme conducted by Monash University and the Australian Catholic University.
Woodlands Junior is another excellent site with a range of games and interactives.