In a new study about to be published in the journal, Appetite, researchers at Unilever found that 97 mg. of L-theanine (an amino acid found in tea) combined with 40 mg of caffeine was associated with improvements in attention.  This study appears one year after the ESFA (European Food Safety Authority) rejected Unilever's request for a health claim for black tea related to improved mental focus.  Unilever is the parent company of Lipton.

Twenty-nine healthy regular tea and/or coffee drinkers participated in the study.  Subjects were randomized to consume either a drink containing L-theanine and caffeine mixed with iced tea powder in water, or a placebo (water with iced tea powder) separated by between 6 and 14 days.  They performed two attention tasks and completed a questionnaire before drinking, and then again 10 and 60 minutes after drinking.

"The combination of L-theanine and caffeine significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved significantly. The results support previous evidence that L-theanine and caffeine in combination can improve attention," the authors concluded.

To give you a little perspective, a cup of tea contains roughly 20 mg. of L-theanine and 40 mg of caffeine, so to get the same dosage of L-theanine given in the study you'd need about 5 cups of tea, but you'd end of up with more caffeine.  A quick search for similar research revealed a handful of recent studies that have been done to examine how L-theanine and caffeine affect alertness, attention, cognitive performance, and/or mood.  Most used roughly 100 mg L-theanine and 40-50 mg caffeine, along with a relatively small group of subjects. 

A 2008 review of literature on this topic published in Nutrition Reviews concluded, "The studies reviewed suggest that caffeinated tea, when ingested at regular intervals, may maintain alertness, focused attention, and accuracy and may modulate the more acute effects of higher doses of caffeine"  (abstract).  It seems that this effect is probably real, but the ESFA said the studies submitted as evidence were "either inconsistent or incomprehensive" (reference).   I think probably as we get more studies, and especially studies with larger numbers of human subjects, we will be able to get more convincing data. Source:  Tea Compounds May Boost Attention Span – Unilever Source: Appetite Published online ahead of print, doi:10.1016/j.appet.2010.01.003 “L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness” Authors: S.J.L. Einother, V.E.G. Martens, J.A. Rycroft, E.A. De Bruin

(Please keep in mind that these findings do not necessarily mean that all or any particular tea will confer these benefits to the consumer.  Tea research is in its infancy and caution should be used when drawing conclusions about the actual health benefits of any tea product.  The Tea Table, LLC does not claim that tea has recognized health benefits.)