grow bacteria on Petri dishes (see the American Society of Microbiologists web page for K–12 lesson plans at https://www.asm.org).
As a suggested adaptation, students could measure nitrogen
levels in the soil prior to planting and again after harvesting the
legumes to measure changes in nitrogen levels for each legume species in each soil type.
Data organization and analysis is an important part of research
and is therefore emphasized in our learning strategy. Data can be
collected initially on paper or the provided worksheet (
Supplemental Material S3 and S4), then sent as a Microsoft Excel spreadsheet
to the instructor for final aggregation. We recommend assigning
basic data-analysis tasks such as averages, minimum and maximum, and standard deviation (see, e.g., Supplemental Material
S5). Simple graphs displaying the means between soil treatments
can be easily made in Excel (e.g., Figure 3).
If the class is capable, basic statistical analyses to determine
whether the relationship between the growth of the legume and
the proxies used for nitrogen levels (chlorophyll levels and number
of nodules) was statistically significant can be performed in Excel
or with free software programs such as the R statistical environment
or MYSTAT. If nitrogen levels of the soil were measured pre-planting
and again post-harvest, students could also look at their statistical
correlation with plant growth. We have included example data for
any data analysis exercise (see Supplemental Material S5). While
we do not provide further statistical advice beyond basic summary
statistics (see, e.g., Supplemental Material S6), we encourage instructors to explore statistical skills with their classrooms more than we
did. One strategy may be to share these data with instructors of
mathematics courses to integrate this work across classrooms.
True to a student-centered learning environment, we administered a post-activity survey to each student to assess student attitudes, learning effectiveness, and self-described skill acquisition
(Figure 4 and Supplemental Material S5). When implementing this
lesson plan, we suggest administering a pre- and post-lesson survey
and assessment to better determine the effects of this lesson plan.
One of the strengths of this framework is the emphasis on furthering a student’s ability to develop testable hypotheses, make meaningful observations, think critically about experimental results,
and draw significant conclusions supported by evidence. Because
one of our goals is to build research skills and scientific literacy
in high school students, we suggest finalizing the project with exercises in scientific writing in which students explain a question of
interest, create a formal hypothesis, describe a method to test that
hypothesis, interpret their results, and ask further questions. This
formative assessment integrates several learning goals and evaluates
the student’s comprehension of conceptual knowledge and the
integration of practical approaches to initiate, design, execute, and
report on research. The ability to think critically and link conceptual ideas with practical methods and the evidence obtained was
the backbone of our teaching framework. Therefore, we recommend that the ultimate goal should be a student-written scientific
paper (we think a great goal would be to encourage motivated students to pursue publishing their work in a high school or undergraduate science journal).
Figure 3. Results (means ± SE) from the class experiment,
showing plant responses to soil treatment (autoclaved = sterile
soil, natural = nonsterile soil): (A) chlorophyll index, (B) plant
height, and (C) number of nodules.