Debugging in Scratch: Download my slides from Scratch Conference

27 August 2019

I'm back at my desk following a fabulous weekend at Scratch Conference Europe, hosted by the Raspberry Pi Foundation at Churchill College, Cambridge. I delivered a presentation on debugging in Scratch, which covered tips and techniques to help educators to find errors in their students' projects more quickly.

The talk included my run down of the most common errors students made, based on my experience volunteering at a Code Club. Here they are, briefly:

1. Local variable created for all sprites, not just one sprite
2. Lookalike blocks (for example, confusing set and change blocks, or x and y blocks)
3. Wrong blocks in wrong brackets (check at the top and bottom of brackets to confirm the right blocks are inside)
4. Blocks in the wrong order (especially with regard to initialising variables after starting to use them)
5. Rogue spaces in text fields ("hello" and "hello " are not equal)
6. Scripts on the wrong sprite (check too for fragments left behind when this is fixed)
7. Duplicate scripts created instead of extending existing scripts (this is unique to using worksheets)
8. Not changing the numbers in blocks (and also, not changing the default menu option in blocks with a dropdown)
9. "It worked a minute ago!" errors (failing to reset to a known state at the start of execution, so the project keeps visibility, variable, costume etc settings from the previous run)
10. Timing issues (not waiting for blocks triggered by a broadcast to finish; multiple green flag scripts without explicit coordination; see my blog on race conditions in Scratch)

I have now published my slides, together with my speaker notes, for this presentation, with more information on the above. The presentation also includes a debugging framework (reproduce, diagnose, fix, learn), and tips for testing a script and exposing what's going on inside it at different points in time. Download my Scratch debugging talk here (PDF). In the future, I plan to write an article about debugging Scratch, but I hope you find these speaker notes a useful format until then. (UPDATE! It's out now. You can download a PDF of my Scratch Debugging article in Hello World here. You can also read my round-up of Scratch Conference Europe here).

You can also find additional Scratch resources in my new Scratch resource centre here!

Get free chapters from my Scratch books here.

Permanent link for this post | Blog Home | Website Home | Email feedback

Dip into the blog archive

June 2005 | September 2005 | January 2006 | March 2006 | April 2006 | May 2006 | June 2006 | July 2006 | August 2006 | September 2006 | October 2006 | November 2006 | December 2006 | February 2007 | March 2007 | April 2007 | May 2007 | June 2007 | July 2007 | August 2007 | September 2007 | October 2007 | November 2007 | December 2007 | January 2008 | February 2008 | March 2008 | April 2008 | May 2008 | June 2008 | July 2008 | August 2008 | September 2008 | October 2008 | November 2008 | December 2008 | January 2009 | February 2009 | March 2009 | April 2009 | May 2009 | June 2009 | July 2009 | August 2009 | September 2009 | October 2009 | November 2009 | December 2009 | January 2010 | February 2010 | March 2010 | April 2010 | May 2010 | June 2010 | August 2010 | September 2010 | October 2010 | November 2010 | December 2010 | March 2011 | April 2011 | May 2011 | June 2011 | July 2011 | August 2011 | September 2011 | October 2011 | November 2011 | December 2011 | January 2012 | February 2012 | March 2012 | June 2012 | July 2012 | August 2012 | September 2012 | October 2012 | December 2012 | January 2013 | February 2013 | March 2013 | April 2013 | June 2013 | July 2013 | August 2013 | September 2013 | October 2013 | November 2013 | December 2013 | January 2014 | February 2014 | March 2014 | April 2014 | May 2014 | June 2014 | July 2014 | August 2014 | September 2014 | October 2014 | November 2014 | December 2014 | January 2015 | February 2015 | March 2015 | April 2015 | May 2015 | June 2015 | September 2015 | October 2015 | December 2015 | January 2016 | February 2016 | March 2016 | May 2016 | July 2016 | August 2016 | September 2016 | October 2016 | November 2016 | December 2016 | January 2017 | July 2017 | August 2017 | October 2017 | November 2017 | January 2018 | February 2018 | August 2018 | October 2018 | November 2018 | December 2018 | January 2019 | March 2019 | June 2019 | August 2019 | September 2019 | October 2019 | January 2020 | February 2020 | March 2020 | April 2020 | May 2020 | June 2020 | September 2020 | October 2020 | December 2020 | January 2021 | February 2021 | May 2021 | June 2021 | October 2021 | November 2021 | December 2021 | January 2022 | February 2022 | March 2022 | May 2022 | July 2022 | August 2022 | September 2022 | December 2022 | March 2023 | April 2023 | May 2023 | June 2023 | October 2023 | November 2023 | January 2024 | February 2024 | May 2024 | June 2024 | July 2024 | September 2024 | October 2024 | November 2024 | December 2024 | Top of this page |