I am brand new to R and a teacher, so thank you for your patience. I've searched many other questions on Likert stacked bar charts ([this one is close](https://stackoverflow.com/questions/43196827/likert-stacked-bar-chart), but not exactly what I am struggling with). I can't seem to find one that discusses how to pull the results of both survey pre- and post-test into the same stacked bar chart. I've read through Hayley's R for Data Science book, examples on GitHub, the R Companion Handbook, and the R Cookbook. Still really need some help, as a beginner. 

I have a set of 12 student questions, each with a pre- and post-test response, on a scale of Strongly Agree to Strongly Disagree. 

My question is: How did the student survey responses change before and after a test?

My data originally was displayed as:

```
Student sex(F=0,M=1)  PreTestQ1   PostTestQ1
1       0              Agree      Disagree
2       0              Disagree   Agree
3       1              Agree      Agree
4       1              Disagree   Agree

```

First, I converted the Agrees/Disagrees to numerical data (Strongly Agree = 1, Strongly Disagree = 4, no Neutral option) and tidied the data from wide to long using:

```
    # Set data frame as wide
msse_wide <- read_xls("ProcessDataMSSE.xls")
colnames(msse_wide) # Displays names of columns
head(msse_wide)

# Set data frame as long, after running wide code above
msse_long <- msse_wide %>%
  gather(question,obs_prepost, c(2:25)) # This pulls the columns from 2 to 25 (not including the "sex" column), test it out first as a precaution

# NOW MY DATA IS TIDY!!!! :)

```

And I got:

```
    > msse_long
# A tibble: 1,824 x 3
     sex question obs_prepost
   <dbl> <chr>          <dbl>
 1     0 1Pre               3
 2     0 1Pre               3
 3     0 1Pre               2
 4     0 1Pre               3
 5     0 1Pre               2
 6     0 1Pre               3
 7     0 1Pre               3
 8     0 1Pre               2
 9     0 1Pre               2
10     0 1Pre               4
# … with 1,814 more rows

```

Now I would like to visualize the percentages of Strongly Agree --- Strongly Disagree responses as a stacked bar chart, using percentage responses, AND comparing pre- and post-test as stacked bars one on top of the other (so, with 12 questions pre- and post-, I will have 24 total stacked bar charts).

The ultimate goal is similar to this example from R Companion:
[Simple Stacked Bar Chart](https://i.stack.imgur.com/i8824.png) ...except I am stuck on how to pull percentages out of my data, and compare pre- and post-tests one on top of the other.