Teachable Moments From Unexpected Lab Results

"Students getting unexpected lab results seems to be a universal challenge for science teachers, with 100% reporting their occurrence in a recent informal NSTA Reports poll. Measurement error was the most commonly cited cause (40%), while 13% said students omitting a step in the instructions let to errors.
When the unexpected results are caused by an identifiable, unintentional error, 42.7% of science educators said they pool the class data and have an error analysis discussion. Thirty-two percent say they have the students use the collected data and note the error and its potential effects." NSTA Reports
Science is not always black and white.  The data is what it is.  This allows for a discussion on the importance of a large data pool.  Its is a teachable moment to address variables seen or unseen or unexpected results and how scientists deal with them.