> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sightlinebehavior.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Add intervention phases

> Record when each intervention started so Compare can group a student's observations by phase.

A phase is a dated stretch of the student's plan, such as a break card from March 3. Sightline places each observation in a phase by its date, so you don't tag observations yourself.

## Add a phase

**1. Open the case file**

Open the student, select **Case File**, then **Add phase** under **Intervention phases**.

**2. Enter the phase**

Enter a **Start date** and a **Phase name**. Add an **End date** once the phase is over. Use **Notes** for what changed.

**3. Save**

Select **Save**. To edit a phase later, select it. **Remove phase** is inside the editor.

## How observations are assigned to phases

* An observation belongs to the phase whose dates include its date.
* Observations outside every phase, such as those before your first phase, count as Baseline. You don't need a Baseline phase.
* From a new phase's start date, observations belong to it, even if the previous phase has no End date.
* Leave Context empty unless the phase applies in one setting only. If you fill it in, the phase covers only observations whose Setting matches it exactly, ignoring capitals.

## Where your data appears

In Compare, once the observations span two or more phases, the Over time chart labels each phase and divides them. The Session record groups observations by phase and adds a Difference from the previous phase: the change in the average. It is left out when the method or interval setup changed between phases. Select a phase's heading to focus on it. See [Compare observations](https://docs.sightlinebehavior.com/comparison.md).

## Good to know

A difference between phases can come from how or when you observed. Before reporting it as a change in behavior, check that the definitions, methods, observation lengths, and conditions match.

## Related

* [Compare observations](https://docs.sightlinebehavior.com/comparison.md)
* [Update the Case File](https://docs.sightlinebehavior.com/case-file.md)
* [Describe results in a write-up](https://docs.sightlinebehavior.com/writing-up-observation-results.md)


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