I speak to a great deal of parents (and teachers!) who are worried that their child confuses the letters ‘b’ and ‘d’. I recently came across a terrific article by Speech Pathologist, Lucia Smith, who has made a point of presenting ways to teach ‘b’ and ‘d’ through comparing, contrasting and using mnemonics. You can find the article here:
http://www.loveandreilly.com.au/images/pdf/bdpq.pdf