New focus and hypothesis: Decimal Place Value

As mentioned in earlier posts my COL inquiry focus is looking at how can I improve my kids mathematical number knowledge using the Learn Create Share pedagogy? In previous months I was looking at increasing my kids times tables knowledge. My focus is now shifting to their knowledge of decimal place value. At Year 7 & 8 the children should be able to add and subtract numbers up to 2 decimal places. Evidence from classwork and conversations with the children highlighted general gaps in or misconceptions about their decimal place value knowledge. For instance:

Adding tenths to the hundredths column.
3.12 + 9.4 = 12.16

I hypothesise this comes from viewing decimal numbers as whole numbers i.e 12 hundredths as 12 and lack of understanding of the base 10 system. I will be looking at ways to address these misconceptions and place value knowledge gaps.