When viewing a Chromebook on a classroom display objects like the cursor, and menus are very small for the screen.
The display size setting in your Chromebook may not have defaulted to an appropriate size for your classroom display
Adjust your 'Display and text size'
The display and text size can be adjusted for any display connected to your Chromebook. The controls for that setting are found in the Device tab of your Chromebook Settings.
Open your app menu (Circle G icon at lower left of the Chromebook screen)
Find and open the Settings app which has the icon of a gear.
Select 'Device' from the list of tabs on the left.
Select 'Display' from the menu at the right.
If the switch next to 'Mirror Built-in display' is on it you should see two stacked rectangles in the 'Arrangement' area. You want that option turned off so the two rectangles are side by side.
The two rectangles represent your attached screens. (They can be dragged around to change how your cursor moves between them). Select the rectangle that represents your larger classroom display. Notice the display's name becomes underlined below and the settings options switch to the display you selected.
Next to the setting for 'Display and text size' is a slider. Drag the circle to the right side of the slider. As you do the rectangle representing that display will shrink. If you make it proportional to your 'Built-in display' there will be less of difference between the two displays.
You may want to switch screen mirroring back on if you prefer your display that way. Your Chromebook should remember the settings the next time you attach to your classroom display but may need to be readjusted for any other displays you connect to.
Watch the video demonstration below.