  EvoGrader is a free, online, on-demand formative assessment service designed
for use in undergraduate biology classrooms. EvoGrader's web portal is powered
by Amazon's Elastic Cloud and run with LightSIDE Lab's open-source
machine-learning tools. The EvoGrader web portal allows biology instructors to
upload a response file (.csv) containing unlimited numbers of evolutionary
explanations written in response to 86 different ACORNS (Assessing COntextual
Reasoning about Natural Selection) instrument items. The system automatically
analyzes the responses and provides detailed information about the scientific
and naive concepts contained within each student's response, as well as overall
student (and sample) reasoning model types. Graphs and visual models provided
by EvoGrader summarize class-level responses; downloadable files of raw scores
(in .csv format) are also provided for more detailed analyses. Although the
computational machinery that EvoGrader employs is complex, using the system is
easy. Users only need to know how to use spreadsheets to organize student
responses, upload files to the web, and use a web browser. A series of
experiments using new samples of 2,200 written evolutionary explanations
demonstrate that EvoGrader scores are comparable to those of trained human
raters, although EvoGrader scoring takes 99% less time and is free. EvoGrader
will be of interest to biology instructors teaching large classes who seek to
emphasize scientific practices such as generating scientific explanations, and
to teach crosscutting ideas such as evolution and natural selection. The
software architecture of EvoGrader is described as it may serve as a template
for developing machine-learning portals for other core concepts within biology
and across other disciplines.
